It's not that I'm unable to afford the Pro version but it contains so much add on stuff that I won't even bother to install.  From what I've learned from a post by Noel, ARA and VST3 support exists in the basic X3 product.  So from that I assume that my existing Melodyne 2.1.1 Editor should integrate into SONAR X3 just like it is in Studio One and my existing VST3 plugins should work as well.
 
I will lose the ProChannel plugs and upgrades that I have in X3.  I don't see that as a problem since I'm UAD2 equipped and I have all the LA2A, 1176s, Pultecs, etc available in UAD and Waves versions.  I've got the tape simulator and channel strip emulators covered by Slate.

I don't get the Addictive Drums but I have every Toontrack drum kit that exists.

I don't get the Lounge Lizard keys but I have EZkeys and I'm not much of a player so the extra tweakablity won't help me any.

I've already got Dim Pro and Rapture.

I won't get the fly out EQ but clicking on the FX bin can fly out the nice EQs I already own.

And if at any time I wish to go whole hog, I suppose I can upgrade from there.

Anyone see anything I missed?

I see an additional upgrade level that Cakewalk should consider - a $25 upgrade that would unlock the Prochannel strip in X3 to use existing ProChannel modules that a registered user already owns.

I could run through the gambit of plug-in counts etc., but SMTPE/MTC and Surround will be missing. If you use a lot of external gear I'd take that into consideration.
 
Also, Addictive Drums is quite nice. Even if you feel that you don't "need" it, I can't imagine you won't want to use it when you start to use it.

I feel the same way!! Only thing is if you have older projects , you know they wont load up the same . I'm sure you used the pro channel on some older projects. $150 I feel all were getting is other developers plugins .. and fixes .
 

The extra $50 is worth it for all you get in my opinion. We aren't adding unlocks. Trying to keep this simple as possible.

I think that the basic version will be a bit incapable, but I can't find any difference other than a few plugins between Studio and Producer.

I believe it used to be that things like Audiosnap were Producer only.  Now the Producer exclusives seem to be a drum sampler, tape effect, electric piano, fake guitar thing, and one Nomad Factory effect.  Most of these are somewhat redundant with existing X3 Studio capabilities.
 
I agree that for someone with third-party implementations of those effects, the Producer edition seems uncompelling. 
 
(edit - for a new user, Producer also offers full versions of good old Dimension and Rapture, and some more effects - but it's quite expensive)

Ryan Munnis [Cakewalk]
I could run through the gambit of plug-in counts etc., but SMTPE/MTC and Surround will be missing. If you use a lot of external gear I'd take that into consideration.
 
Also, Addictive Drums is quite nice. Even if you feel that you don't "need" it, I can't imagine you won't want to use it when you start to use it.

Agggh, SMPTE/MTC, although I haven't chased time code in forever and a day.  If I run into a project that needs that, I can always back down to X2 Pro or run one of my other platforms.  I'm just trying to find a reason to buy ANY Cakewalk product at this time.  (No insult intended but the Take Comping and ARA implementation are the only bullet points that caught my eye.)
 
As far as another drum product, I'm tempted sometimes to eliminate some of the libraries I already own just so that my choices are more limited.

For those weighing option, $99 Studio is a good in between of you want ProChannel. Just presenting facts. def options

Mod Bod

Ryan Munnis [Cakewalk]
I could run through the gambit of plug-in counts etc., but SMTPE/MTC and Surround will be missing. If you use a lot of external gear I'd take that into consideration.
 
Also, Addictive Drums is quite nice. Even if you feel that you don't "need" it, I can't imagine you won't want to use it when you start to use it.

Agggh, SMPTE/MTC, although I haven't chased time code in forever and a day.  If I run into a project that needs that, I can always back down to X2 Pro or run one of my other platforms.  I'm just trying to find a reason to buy ANY Cakewalk product at this time.  (No insult intended but the Take Comping and ARA implementation are the only bullet points that caught my eye.)
 
As far as another drum product, I'm tempted sometimes to eliminate some of the libraries I already own just so that my choices are more limited.

Well, if those two are the only ones that caught your eye and you already have a lot of the included plug-ins, then I can tell you those are the two I'm personally most excited about and can say they're by far the biggest enhancements in my personal world.
 
Dragging and dropping a clip from an audio track to a MIDI track and it converting automagically? LOVE IT! I'm not a huge fan of guitar MIDI controllers and I'm awful on keys, so this helps me tremendously to lay down a melody and then drive a synth with it afterwards.
 
Also, I drink too much coffee and am way out of practice on guitar, so I tend to have to record multiple takes. The comping improvements are pretty slick when you start auditioning and promoting multiple performances in real time.
 
If those are the two features that stuck out to you, I'd say they're really good ones to be excited about. That's my opinion at least.
 
I will say the other thing I personally didn't know if I'd be using a lot were track colors, but now that they're there I can't stop. It's super helpful for organizing my sessions and the UI makes it very easy and quick to deal with. 

Also, personally I'd never go back to not having ProChannel. The flyout EQ is ridiculously nice.