Upgrading for the future

My current system is really beginning to show its age:
Athlon 64 3700+ San Diego OCed to 2.8
MSI 7207 Mobo
2 GB Corsair XMS PC3200 DDR Ram
EVGA 7900GS KO OCed 605/815

Now comes my Dilemma. I have an E8400 Wolfdale I got from work for free. I was planning on just getting a new mobo and ram for it. I was looking at some prices and for a few dollars more, I could get a Phenom II X3 720BE, mobo and ram for a few dollars more. The Video card I am not concerned at the moment, as that can wait till christmas.

I have been running my current system for the last 4-5 years now and it has been very good to me. I am looking to get 4-5 years out of my next build. I am not super gamer of the year, I usually play Warcraft and possibly Diablo 3 when it comes out. Would I be better just building a new AM3 based system or would the E8400 wolfdale have the ability to last, I have heard the 775 sockets are on their way out the door in the near future.

Thanks for all help.

I don't think Intel has any more CPU releases scheduled for Socket 775. The E8400 would get you by just fine for a year, maybe two, but almost certainly not 4-5 years. The AM3 Phenom II based system if it is about the same price, on the other hand would most likely allow you another CPU upgrade in the future.