In the end it all depends on how they program it. If they make every "sprite" an AI thread, then yes it might require a lot of CPU juice. Then again, if they use old single-threaded AI schemes and pile-up the eye-candy, it will require lots of GPU. My guess is that it will be more like Supreme Commander and tend toward the use of multiple cores so your quad CPU is good to have.
As for video, I would suggest to wait unless you have good reasons to buy right now. Since there is no release date yet (or even release quarter), we can safely assume it won't be out for at least 6 months. Video card prices will drop a bit more and we might even have a new wave of cards out from ATI (32nm).