It all depends on what you are going to be doing with your machine. Right now, I don't feel that you're paying through the nose for a Quad, you can get a 6600 or 9550 pretty cheap nowadays, so what if it's only marginally faster than a dual, you aren't getting fleeced and if and when more games do start taking advantage, then you will be set. I know people have been saying this for a few years now and it's getting to be a tired argument, but it's up the user, you aren't making a "bad" choice either way.
For someone like me, who upgrades pretty infrequently, there's no reason not to go quad, in fact there's no reason not to go i7, which is what I did. I am all over Empire when it comes out and built this machine more or less for that game. I just don't think my Opteron 165/8800GT is up to the task at 1920.
Now if it turns out that Empire doesn't care whatsoever about my two extra cores or extra bandwidth, am I going to be disappointed? Not in the least, I'll find a use for the extra cycles, no doubt about it. I'm going to be running this machine for 3-4 years with some GPU upgrades in between, so it's completely worth it to me.