HEYO! I have a 630i too! I got it from my buddy and gutted the internals for new stuff.
If you are going to get a new computer, I would highly recommend keeping the 630i case, since its really cool. Of course, its all preference, but being able to control the lights and stuff is pretty cool. Even with a new motherboard I am able to control the lights and everything fits nicely. Remember though, if you do choose to re-use the case, you would need to run a Nvidia GPU for the light changey thing to work.
I still run the E8400 that came in it in a different computer, and I run it with an older GTS250 SLI setup. I mean, what you can do if you want is to get a nice GPU right now and throw it in there, and then when you decide to get a new processor and all, you can use the graphics card you bought to go with it.
Do you have a budget?