Sure. Upgrade the whole thing if you feel like selling your current rig. I was thinking you sounded "value-minded" and wanted to know how best to spend a little (or a lot of) cash to improve gaming performance.
Too many people are upgrading, spending huge cash, and in the end the performance gain that they can see (maybe 10%) makes them feel unsatisfied. I've been there, done that, and now when I upgrade, I get rid of the old platform completely and go with the latest, ie from 775 to i5 or i7 which I haven't done yet.