I would think it reasonable to work out exactly what benefit SP2 would bring to the table before deciding whther or not to install it. As I understand from the kb articles, among other things it enhances device connectivity as new standards emerge, better resource management for sidebar gadgets & blu-ray recording capability.
Personally, I think if it ain't broke, don't fix it & I know plenty think Vista is broke out the box
but mine has always coped well enough. I think I'll leave it for now.