By running a 64 bit OS you loose nothing and gain the ability to use more memory plus 64 bits offers better security and a smoother, faster over all system. The only reason not to go 64 bits is if you have hardware that does have 64 bit drivers.
You can run 32 bit programs in a 64 bit environment but with the OS being 64 bits you can also run 64 bit programs. If you run X2 64 bit most plugins should be 64 bits now. Those that are not can be bitbridged. Or a newer substitute can be used. It just a small problem now. Its no longer the problem it once was.
I went 64 bit with Sonar 8. I wouldn't go back to 32 bits.
The thing to think about is that few people that moved to 64 bits have gone back to 32 bits.