it's difficult to tell if it's overly worn in that pic, but it definitely looks old. my philosophy is that if you're not sure, replace it. i recommend replacing both sprockets and the chain at the same time.
if your current sprocket is really +3, that will get you quicker acceleration than stock. everyone's got an opinion on if that's overkill for the street or not. i think it is, but that's just me.
it seems that most people that change their gearing like that go for the -1 front, +2 rear (which i also think is overkill for the street). most also go for the 520 conversion, which gives you a bunch of quality options on gearing and brands.
i highly recommend calling up the folks at STG and talking to one of their experts about the kind of riding you do in order to match your new chain/sprockets/gearing to you. they're good people.
hope this helps...
s3aturnr