Cubase 9.5 has no support for 32bit plugins.  If you want to use any 32bit plugins you'll have to get jBridge or something else.
 
The MIDI VST thing is more complex.  Here's what I've been able to put together (and I'll admit I may be missing something here, people talk about things like plugin APIs but they clearly have no clue what they are saying, I write code for a living so I tend to be really picky about details):
1.  VSTi instruments that generate MIDI work just fine in Cubase 9.5.  They work/it works just like SONAR Platinum.
 
2.  Long, long ago Cakewalk came up with a MIDI plugin format, MFX.  This was pre-64 bit DAWs.  A number of MIDI plugins were made for it.  At that time Cubase wrote an adapter so you could use those 32-bit MFX plugins in Cubase SX.  But this was only 32-bit.  And was never officially supported.  With Cubase 9.5 not having ANY 32-bit support, it's dead.  And a 64-bit version of the MFX wrapper was never made.  So while there are 64-bit MFX plugins (which SONAR platinum uses -- it doesn't do 32-bit MFX any more either) none of those work in Cubase.  Here's the link to the adapter, but it's 32-bit only and doesn't work in Cubase 9.5
https://www.steinberg.net/en/support/knowledgebase_new/show_details/kb_show/using-mfx-plug-ins-in-cubase-nuendo-pc-windows/kb_back/2020.html
 
3.  Cubase has its own MIDI VST plugin format called, VST-MA.  There are actually commercial plugins written that use it.  Frank's MIDI plugins come in MFX and VST-MA format for example.  It's not a secret, it is documented.  But few/no other DAWs ever added support for it, so people seem to see it as something less.  Even though Cubase comes with a bunch of plugins that use it.  It is what is necessary for a plugin to show up in Cubase's MIDI insert menu.  No MIDI generating VSTi instruments will show up in the MIDI insert menu.
 
So what does this mean?  Saying Cubase doesn't support MIDI VST isn't true at all really (VST-MA is MIDI VST).  Cubase 9.5 works pretty much exactly like SONAR Platinum does as far as what most users would call MIDI plugin support.  Soft synths that generate and process MIDI work just fine, you can route their input and outputs all day and night, just like in SONAR. 
 
The "real" complaint seems to be that there is no way to insert a VSTi that generates/processes MIDI into the MIDI insert on tracks in Cubase.  Just like you couldn't insert a VSTi that generates/processes MIDI into the MIDI FX channel in SONAR.  Some people want this and keep talking about MIDI VST support like it was a real thing that somehow Cubase is missing.
 
While I can't use (for example) any of the tencrazy.com MFX plugins in Cubase, every single VSTi that generates and processes MIDI appear to work exactly like they did in SONAR.  And in theory I could develop my own VST-MA plugins and they would show up in the MIDI insert list in Cubase.  Frank's MIDI plugins do and they work fine.
 
So I think this is not a real thing.  Cubase does support MIDI VST plugins, just not some sort of bizarre hybrid that would let you use a VSTi (like say Kirnu Cream) without having to have extra tracks/etc.  I don't think any DAW does this treat a VSTi as a MIDI effect trick, though I don't think it's impossible.
 

My biggest complaint with Cubase Pro has to do with the quantizing function, specifically the swing %. With Swing at 0% the beat is straight, at 100% the beat is swung as a perfect quarter note eighth note pattern.... The problem is the lack of ability to Over-swing where the second note goes more than 2/3 of the way to one following. This is used primarily for Jazz ride cymbals and also for EDM. In Sonar, 50% swing represents Straight eighths, 66% is a perfect swing (same as cubase 100%), going up towards 100% in Sonar will actually get the second note all the way up to the third note, as Over-swung as you want. (Try 68%-70 swing on a jazz swing song and see what I mean) In Sonar, values below 50% will under swing, giving a slight rushing of the second note. I have used over- swinging and underswinging on countless songs and find that function very valuable. Go figure the first beat I put down in Cubase Pro was a shuffle and I was saddened to not be able to over swing it!! 😞

My second biggest complaint is seeing quite a few of my 64 bit plugins blacklisted in the plugin manager and not letting me restore them.

That's just my first impressions. I need a program the Really Swings!!

Really appreciating what I have in Sonar! (keeping hope!)

raisindot
I decided that if I do switch Cubase is the one I'll go to because I primarily build compositions in MIDI and then output audio tracks from my sound modules and VSTs. 

 
Exactly my workflow too.
 
Tip:  The GUI MIDI Device Manager does not work for adding devices.  It's another known bug that's gone unrepaired for years.  If you have to add a MIDI sound module that isn't already among the Cubase defaults, you'll want to create a "patch script" (.txt file).  Look in C:\Users\<username>\AppData\Roaming\Steinberg\Cubase 9_64\Scripts\Patchnames\inactive (for example) and copy one of the supplied files and modify it to suit.  Check out the script documentation.txt file for help.  Restart Cubase and the device should appear in the appropriate list.  BTW, these files can also be found in C:\Program Files\Steinberg\Cubase 9\Scripts\Patchnames\inactive, but it appears to be a backup - changes made there won't appear in the program.
 

raisindot
I find the interface absolutely inscrutable. For example, if took me forever to figure out how to get my audio interface to be an output (instead of the stupid generic ASIO driver thing). When you have to look up online help for something as simple as this, trouble is a'comin'. 

 
Yup.  And I'm sorry to say it doesn't get better 'til you've worked through every nuance of your routine, learning the Cubase way and optimizing settings to your workflow.  Then, it becomes apparent that Cubase can do pretty much anything you throw at it, so long as you have the time and patience to figure it (and the various workarounds) out.
 

raisindot
One question i had based on the original post is he said the legacy MID VST programs won't work with Cubase? Does that mean that all of this many VST plugins I have, from Dimension Pro to Lounge Lizard to Arturia Keyboard V, won't work in a MIDI situation with Cubase? That would be a total deal-killer. 

 
To repeat what Matt said, those are VSTis (VST Instruments) and should work just fine, so long as they're 64-bit.  DXi is not supported, so Sonar users should expect to see a handful of Sonar-bundled plugins disappear.  Others, like the Blue Tubes collection, appear to be earmarked for Sonar and also will not load into Cubase (or any other DAW).
 

msorrels
The MIDI VST thing is more complex.  Here's what I've been able to put together....

 
Excellent summary of the situation!  Thank you, Matt.
 

msorrels
The "real" complaint seems to be that there is no way to insert a VSTi that generates/processes MIDI into the MIDI insert on tracks in Cubase.  Just like you couldn't insert a VSTi that generates/processes MIDI into the MIDI FX channel in SONAR.  Some people want this and keep talking about MIDI VST support like it was a real thing that somehow Cubase is missing.

 
Personally, I just want to load the Piz MIDI plugin collection and other (presumably MFX?) MIDI VSTs into Cubase's MIDI Inserts.  If everything you've discovered re MFX vs. VST-MA is accurate, then I'm guilty of assuming MFX to be the 'open standard' while Steinberg's MIDI Inserts are more-or-less proprietary.  I guess that's wrong and we're just stuck with an unfortunate VHS vs. Betamax situation.  Yeah, we need an MFX-to-VST-MA wrapper.
 
BTW, one of the other workarounds I've seen discussed is MIDI port piping applications (e.g., MIDI Yoke) that allow for standalone applications (e.g., MIDI-Ox) to process MIDI data on the fly.  This gets pretty complicated and I'll confess I haven't had the guts to try it on my mission-critical workstation yet, but it's an option for anyone desperate to add CAL-style scripting to Cubase, for example.
 

Blogospherianman
My biggest complaint with Cubase Pro has to do with the quantizing function, specifically the swing %. With Swing at 0% the beat is straight, at 100% the beat is swung as a perfect quarter note eighth note pattern.... The problem is the lack of ability to Over-swing where the second note goes more than 2/3 of the way to one following. This is used primarily for Jazz ride cymbals and also for EDM. In Sonar, 50% swing represents Straight eighths, 66% is a perfect swing (same as cubase 100%), going up towards 100% in Sonar will actually get the second note all the way up to the third note, as Over-swung as you want. (Try 68%-70 swing on a jazz swing song and see what I mean) In Sonar, values below 50% will under swing, giving a slight rushing of the second note. I have used over- swinging and underswinging on countless songs and find that function very valuable. Go figure the first beat I put down in Cubase Pro was a shuffle and I was saddened to not be able to over swing it!! 😞

My second biggest complaint is seeing quite a few of my 64 bit plugins blacklisted in the plugin manager and not letting me restore them.

That's just my first impressions. I need a program the Really Swings!!

Really appreciating what I have in Sonar! (keeping hope!)

 
Now admittedly I'm tired and not that bright to begin with and therefore I'm probably talking through my hat, but wouldn't a viable workaround to be to reverse the clip, apply the "mirror image" of the swing amount you want, and then reverse it back? 

I've spent a week now methodically reading the 1000+ page manual, trying out many things I read. Meanwhile I set up a few projects, imported some stuff from Sonar and generally tried to get a feel for the program. I think I plunged into Cakewalk head on, many years ago, and never fathomed the depth of the software. Now at least I want to see all the possibilities, whether I'll use them or not.
So far, I've been able to get what I want from Cubase and the learning curve isn't too bad. I think the problem is more to let all the procedures sink in and become second nature. And, admittedly, Cubase doesn't really help with some weird UI choices, although I'm not really sure whether they're weird or simply different from Sonar.
In a sense this turns out to be an opportunity. I've never studied Cakewalk in-depth, as I was still learning about audio and midi. Getting results had priority, no matter how roundabout the way. And those ways turned into common practice. Now I'm forced to study the DAW and as long as Sonar works, I've got time on my hands.

My short experience, 2 hours, with Cubase pro is positive.
Biggest hazzle so far was the activation.  
Audio and midi setup was a walk in the park. Plug 'n' play sort of.
It's hard to navigate but it'll come. 
Cheers!

Resort Records
The Good:

• Strong MIDI support.  Cubase began as a MIDI sequencer in the 80s and, consequently, has thorough MIDI support. 

The Bad:

Audio takes.  By default, overlapping audio takes in a single Cubase track mask previous takes.  By contrast, Sonar will play overlapping takes.

Good information, thanks for sharing. Just two little points though, Sonar also started out as a MIDI only sequencer in the 80s, not important, just thought I'd mention it.
 
I always thought Sonar's handling of audio takes was the dumbest thing ever. The occurrences of me wanting clips piled on top of each other to play at the same time are vanishingly rare, and it always caused much time wasting when copy/pasting or dragging a clip to somewhere else, where I had to go in and remove the underlying pre-existing audio after. Add that to it's awful xfade editing, and it was a complete chore to edit audio. It didn't really matter what you set your drag and drop options to, there were always occasions when it did something you didn't want. Track lanes were just horribly broken.
 
I edit audio day-in day-out, and my chosen platform is an audio-only editor (I used Sonar for MIDI sequencing and occasional mixing, it had some REALLY neat features in the mixer, and when I sadly, really need to use audiosnap on dodgy musicians). I've yet to find any combined sequencer-based "DAW" that gets editing right, the first one I see that does will be where I put my money to move away from Sonar now that it's gone.
 
However, Sonar got it's MIDI editing pretty damned good. I always end up with a brain aneurysm when I have to work in Reason's sequencer, it's a complete and utter PITA since some refresh several versions ago. I believe Cubase used to work on a very similar workflow to Reason (didn't Steinberg interfere with Reason's design or something?), where you have to create clips first before putting anything in them, and all the weird copy/paste drag/drop, how fluid is its MIDI editing now?
 
Also, a BIG show-stopping issue for me...
How easy is it to export individual audio files from start to finish, for each track? Sonar does this magnificently, some other DAWs seem to believe they exist in their own little world where nobody using any other software will ever collaborate with its users. Project (or at least project data, including rendering softsyths) interchange is an absolute must for me.

Been working in 9.5 for nearly two weeks now.  Once you get past some of the workflow differences, I'm really liking what's there.  The biggest plus for me is that there is a real console strip in Cubase, that can work alot like ProChannel did.  The control room stuff is really cool too.  I'm trying to use that setup with my XR-18 live mixer, because I have way more I/O on that, than my focusrite, and I have an in-ear rig setup in my studio with a 6 port headphone amp.
 
Still on the learning curve with this thing.  I just have been watching a ton of youtube videos trying to soak up as much as I can, and going through and remixing old Sonar projects.  I've really been happy with it though.  They've made some great adjustments since I last used Cubase which was ver. 5.

bartveld
I've spent a week now methodically reading the 1000+ page manual, trying out many things I read. Meanwhile I set up a few projects,

I think that's a great method. The trouble is that the Cubase operation manual is long on description and short on procedures. To fill this gap, I've ordered The Complete Guide to Music Technology Using Cubase 9 from lulu.com.

Don't forget Groove3 as well - I've not looked at their Cubase tutorials but the ones I've watched have always been excellent.