Based solely on my experience, I'd say wait.

I installed SP2 q few days ago, but uninstalled it yesterday.

I had no internet access for 24 hours after installation, then several programs were constantly seeking internet access (esp alg.exe & svchost.exe) it seemed like some very determined nasties had got in.
It got so bad I was planning to completely re-install XP, but as the PC has behaved well for 24 Hours - I'll wait to see if things stay quiet.

With an independant firewall/virusscan/spyware (not they're perfect) I'm gonna need some convincing to try SP2 again.

Tricky decision.

H