Reminds me of something I read on a photography site:
Is it worth it?
Specifically:
"Something is worth it if its benefit exceeds its cost - to you. That's easy to answer if I know you, what you shoot and your situation.
I can help you understand what's new and why anyone would care, but only you know how much money means to you and whether or not you use the features that may have been added."
I would ask yourself if you don't like the way games play on your current card, and the upgraded performance (check benchmark lists) are worth the money involved, go for it.
Personally, I would wait until the games you want to play don't play at settings that you like before upgrading. For me, that would be pretty low settings: ie: once I don't meet requirements anymore. YMMV of course.
Edit:
One other thing unique to computer systems: the longer you wait, the more you can get for your money because specs keep going up all the time.