I was looking at the same reason you were. I didn't have a clue Cakewalk had a new version coming out, I've been too busy with my new iClone 6 version. I've been with Cakewalk since Cakewalk DOS, and I always got notice of when they had a new version up until now. To be honest I was looking to upgrade by now. I use a lot of midi and audio channels and now and then a instrument would not start for a note or two randomly. I adjusted a tweaked everything, disabled when I remembered other drivers etc. Never was completely satisfied. Bought a new MB 2 weeks ago and Win7 pro to upgrade to 32GB of memory, and I still had same problem now and then. I downloaded Sonar Platinum last night and so far it's great. I'm knocking on wood. I been searching all over to see if they changed their audio engine or CPU processing method, but to no avail. Yes they added a vocal thing which I haven't figured out how to use and a new reverb which took awhile for me to find because it is only available in the Pro tools channel, but it's nothing that special to me. I'll try the new Sonar again later, but if this program stops the sometimes initial dead audio track, it's worth the price me. Then it's what I been hoping for. If my Sonar X3 Pro was working fine like your system, I would not have upgraded.      

Why Should I Upgrade to the New Sonar?
 
Because you want to.

Only you know why you should update.

But you know??? The new system iCons are really really sexy.  Is there a better reason to upgrade!

Anderton 
But most people are upgrading solely for the new amp sims . Okay, not really. 

Yeah..come wipe the beverage spewage off my monitors now, pleeze....
Always a class clown, isn't there?

If you can imagine moving to another DAW in the next year, then NO, do not upgrade Sonar. Spend your money and time with the next program.
 
If you are a dependable CW customer, it is your responsibility to purchase the new program as soon as you can. At $200 per year, $20 per month, 66 cents per day, this is a no brainer. Do not waste any life-time to other than purchasing.
 
Based upon the number of hours I get to play with sonar per week, I figger this update will cost me about $7.70 per week. How can I complain about this?
 
I have been purchasing the top version of sonar each year. So I have been gifted with all the freebees.
 
Our upgrade dollars are a reward to those we have chosen to do this work for us.
 
Not to be insulting:::: If you even think for a moment you are paying for the included content instead of the DAW program I suggest you move to another program.

So obviously I'd be expected to say wonderful things about SONAR but...I finally finished the 2 hours of live recordings from CES from two different artists on three different nights, all 96/24 stuff, quite a bit of ProChannel and plug-ins for imaging and such because I was getting a feed from the FOH mixer (which as you know mixes for the audience, not a recording studio). I have to say the experience in Platinum has been exceptionally smooth. No crashes, fidgeting, weirdness, freezes...nothing except it just kinda purred along.
 
I haven't had a chance to play with a lot of the other goodies, though, and I'm kind of salivating as a read about the new reverb, the PRV improvements, AD2, etc. 
 
I do think the team's efforts to eradicate bugs is making some serious progress.

Is it fair to say that the audio engine appears to be a little smoother than X3e (if that is possible)?  For instance, does it improve latency performance?

Don't bother upgrading is my advice. The hoops you have to jump through to install the damn thing ain't worth it. Believe me. Platinum itself looks like a joy but addicted drums 2 is, well, a bloody nightmare to install. If it is indeed possible to do.
 

I haven't heard of anyone else having a problem with AD2... I sure didn't! Your experience is unique or it would have been all over the forum for awhile now...
 
Such situations often turn out to be user error or rare/messed up system, not cakewalk... as Scook suggested, you should contact XLN... they are very responsive to even stupid questions like a few of mine have been...
 
I had AD1 one on X3... followed the instructions for AD2 on platinum...totally easy, slick and transparent...
 
Thus, I think anyone should ignore your advice as it is a one off experience and so far it is unclear why it is happening... Rather than take personal responsibility and figuring it out you come over to this thread and say "believe me"... I say, "no way"... Do your homework...you haven't... betcha it's the ole user error...(I've made lots of them and in the end... wacked my head and went "Doh!"