but... I already upgraded and I still feel inadequate... what gives?

Your keyboard is too small?   
 

When you upgrade, you risk all sorts of new issues.  New bugs that didn't exist before, new compatibility problems, and new ergonomics (sometimes) to deal with.   I never upgrade in the middle of projects.   That's asking for problems, even with projects without deadlines, why introduce new problems?   Isn't composing and producing good music challenging enough?
 
The other issue is the confusion between one's tools and one's craft.  Skills acquired using software and audio equipment are not the same skills that are involved in the composition and orchestration of music.  I tend to think a lot of people invest more time in their computer skills than in their musical craft, and of course it shows.  Is there anything you need Sonar to do that you cannot do now?  Does the newest version change that?   If yes, consider upgrading, if no, better to spend your time honing your musical skills, writing and producing music. 
 
Other than the very temporary thrill of getting and installing a new piece of software, you're going to spend money and time that often end up with no real advantage (to you, not the software company who will gladly take your money), other than the rapidly diminishing feeling of having the "newest".  I used Sonar 7 for over 5 years before even considering upgrading.   Now I use X3e and will continue to use it for probably another 5 years.  Since CW refuses to fix the bugs in the staff view, where I spend most of my time sequencing, there's no justification at all for upgrading, other than the emotionally-driven gear lust that makes you like everyone else.   Gear lust doesn't produce great music, that should be obvious.
 
If it isn't broken, don't fix it.  If it is broken and the new version doesn't fix it, don't upgrade. 
 
Jerry
www.jerrygerber.com/symphony9.htm
 

To give a sense of perspective, some people are still using 8.5 and happily making music. Fatboy Slim used an Atari until a few years ago. And I'm driving a 15-year-old car because it still gets me from point A to point B.
 
However, if you choose to upgrade remember you can run Platinum side by side with X3e, so you can use X3e and learn the new features in Platinum at your leisure. The two "must have" features are VocalSync if you need to match overdubbed vocal audio to existing vocal audio on video, and if you have clients who want you to generate multiple mixes, MixRecall is huge. If you use AudioSnap, it's been improved.
 
If you use the Vienna Symphonic Library, the VST3 implementation now supports MIDI input buses. In terms of "nice but not necessary," the new control bar is a huge improvement for workflow, especially if you're working with a single monitor. I do a lot of archiving so the DSD export is helpful.
 
But most people are upgrading solely for the new amp sims . Okay, not really.
 
Speaking of upgrading, here's a tip for operating systems. I have my OS on a removable drive. When I get a new OS, I do a fresh install on a new drive and migrate stuff over slowly, for example, re-install something on the new OS in down time between sessions. Eventually I transition to the new OS. The only time that didn't really make much difference was the transition from Vista to 7, I bonded with 7 immediately. But with the XP to Vista transition, it took a while for Vista updates to catch up. 
 
 

I had essentially the same add-ons as the OP.  I upgraded to Platinum and work flow was seamless.  Upgrade was quick, the layout and work flow is essentially identical, just with some improvements.  I actually find it easier to use with the minor layout improvements.

Why Should I Upgrade to the New Sonar?

 
Because you did the research on the product and found that the new features are what you want or need?
 
After that I have no knowledge of why you should or shouldn't upgrade.

If everything is fine and you don't find yourself salivating for any of the new features, I'd say just stay where you are... Cake is going to be rolling out periodic real time improvements and when these things reach a "oh, I gotta have that!" level for you, upgrade!  You'll be ahead of the game, in the sense that you now have a full year of ongoing upgrades from the moment you upgrade and if you do this in six months...you get more goodies than those of us who jumped as soon as we got our invitation!
 
Really, it's a win/win situation from where you're sitting...Personally, I just did it cause that's what I do.  But I was totally in bliss with X3 so really didn't need to and if I were more concerned about money or bang for the buck, I'd have waited. However, I hate the whole money racket, don't have any because of it, and love the bakers and my daw so I just did it.  Crazy, I know... 

In all fairness I didn't read everything above but for me the most compelling reasons were:
 
The collapsible tool bar, Mix recall, the new stackable effects bins and sends, Vocal Sync, midi stretch and the AD producer bundle. For me it was a no brainer value wise. I'm have been an AD user long before it became part of Sonar. The producer bundle is worth the price of admission alone. The Rematrix reverb looks cool but I haven't taken it for a spin yet.
 
As pointed out above you can happily continue making music with what you have. The argument about new bugs etc. doesn't hold water here as this has been the smoothest Sonar upgrade for me yet and I started with Sonar 1 in 1900.
 
Good luck with your decision!!
 
Rocky

Just to add to what everyone loves about the new Sonar: I love the pattern tool!!! Makes it sooo easy and fast to lay down drum tracks!

I can only say.... Sonar 7 was at it's time awesome... I had two 15 inch screens and I allways felt like I needed more screenspace. But those screens are like lightbulbs... And I get blinded after a while. With Platinum I have screensets wich will fit on one 15 inch screen and it works fast. I can adjust my screens with ease... The new screens resize beautifully. Since I installed I have no issues. And.... It's just fun. 
 
With Sonar 7 I was allways looking for VST-i's. I now have 2 external VST-i's. One is a Memorymoog emulation. The other is a midi to VST-i converter so I can play a synthesizer with my guitar. Everything else is in the program. It's there... And it works... 
 
So I get done at the screen what I need to get done there. Then I hit record and I go focus on what's in the room, my instrument, lyrics... And it just works. No hickups...  Sonar is allso great with touch screens... Works awesome with Windows 8. And I think it will work awesome on W10 too. 
 
And you know what.... I love surprises. With X3 Sonar gave me a bunch of stuff like sounds and extra's during the period they were developing it up to X3E. And I loved it. Now with Platinum there will be more treats.... It's so funny.... I get all giggly about it everytime. And... Well even a new car doesn't do that anymore....