I'm tempted not to upgrade, I have recently JB the phone so have all my cool text tones now, the camera is crap but with 16gb the memory is fine. My screen resolution is fine.
I'm thinking iPad!
With the new processor in the iPhone developers are going to take advantage of that extra power. Think how slow your apps/games will run on the 3G compared to the iPhone4.
If your eligible for an upgrade there is no reason not to get it. Your 3G is worth at least $200 at a minimum on craigslist. Figure in 9-10% for tax and you get a new phone. It would be stupid not to upgrade because you "like your text tones"