Hi Carlo,
I had the same issue. Was using X3 and Sonar Platinum was just around the corner. I only had a 128GB SSD for my C drive, but had a raptor drive that I was using to house all of the folders for Sonar.
So, I transferred my C drive to a new SSD (500 GB) and got Sonar Platinum. Just for the record, it was worth it.
I too write most of my projects with VSTs and SP has more to offer here as well.
The PRV and midi have been revised (somewhat) leaning towards improved workflow. You might want to take a long look there.
Of course, if what you have works just fine, don't break it by any means.
Just know that the leap into the next version isn't so painful overall.