whether or not to upgrade?
that depends on what you need it to do, and your budget
AMD will only sell 64-bit processors next year, and it's good not to be 'left behind' in technology (hides my 500MHZ box while nobody is looking) but then again the 2500+ is still powerful enough to play games like Farcry, although games like that depend more on video cards than CPU.
for upgrades, I agree that you'd be better off getting a better GFX card than a mobo+CPU
the Radeon 9800 pro's are getting pretty cheap now
although it would do you good if you did upgrade to a 64-bit processor