I had the Release Candidate SP1 installed a couple of weeks ago, and I still don't know where the improvements were. The overall performance of the system was still sluggish, although the SP1 claims to be a performance update. Ok, firewire was a bit faster on SP1, but that's about it. Vista is also not more stable with the SP1 than without it.
If the original release of Vista could not convince you to upgrade, then the SP1 won't change your mind.
If the original release of Vista could not convince you to upgrade, then the SP1 won't change your mind.