I am thinking about upgrading to SONAR PROFESSIONAL from SONAR X3 Studio and I am wondering if it is worth it?  Is SONAR PROFESSIONAL more stable, have better overall enhancements?  Thanks for any help.
 
 
Liquid Noise 23

There are significant improvements in the new Sonar Professional.

Why not check out all the link here.

http://www.cakewalk.com/Products/SONAR
Then click the link Compare Versions.
Further down the page click See All the new Features.

As for stability most find it at the very least as stable as X3e. I certainly do. The member ship program is also working well. You will get the full benefit with Platinum but there's certainly a lot to recommend the Professional version. While there's quite a few complaints, many are new users and many of the thread will become marked as Solved as issues get worked out.
Cakewalk has also been very proactive in making sure they are fulfilling their promises made regarding the new membership program with monthly updates, fixes and more content.

For $99 it will keep you up to date and add a few things that were in Sonar Producer X3. 
Coming from the same upgrade path as you I will say  there's very little difference. Both x3 Studio and Professional are very stable. You get more stuff and you have to decide if you can use it or not. It's good to keep up to date at this price.  

Thanks for the advice everyone. I have a feeling that I will upgrade.