Welcome back!!!
First wow still have VS7 installed, I almost have you beat, I still have VS8 installed. A while back, just for fun I re-installed VS 5, yep that's Five, on my WinXP machine, and it worked fine.
Now the big question, why should you upgrade to VS X4...
The big main difference is IF you don't use another DVD authoring program, like Nero, Corel resorted back to using the integrated DVD burning module. Something that you probably noticed in VS X3, where you have the awful DVD Factory 2010, or at least DVD MF 7SE.
With VS X4, you can now place titles on any video track, AND use transitions with them. There were some problems with the High-def in VS X3, that seems to have been ironed out in VS X4. Render times are suppose to be faster, I haven't really ran any tests in that regard to know if it really is or not. The Instant Project templates can be packaged and shared. In other words if you create some special templates, you can package them up and share them with others. They added the ability to create
simulated 3D videos. I don't think that you can actually edit 3D video, that was recorded on the newer 3D camcorders though. You would need to purchase the box version to get the free 3D glasses, which are not the old cheap paper types, they are a good quality plastic frame glasses. They also have the Stop Motion animation, and Time-Lapse.
Well that's a start, let's see what others say. There are problems that some are having, nothing new, there's always going to be some problems.