The only tangible benefit SP3 has to consumers is that all updates for the OS up to March 2008 are included. New features like network access protection compatibility and "black hole" router detection algorithm are really only for enterprise users.

If you don't mind installing eighty or so updates after a clean SP2 install then you shouldn't bother with SP3. You can always use a program called nLite to extract your XP SP2 disc to your local machine and then slipstream SP3 into the installer and reburn the image to a blank CD.