Don't hold off any longer.
The only parts that need constant upgrading on the PC are video card and RAM. I'd suggest getting 16gb honestly.
I'd also suggest you get the 7970 unless you hate AMD. It's performs incredibly well according to most benchmarks and easily stacks up and sometimes surpasses the 680 and is only $19 more than the 670 OC.
EDIT: According to MSY it's actualy $4 cheaper to get the OC gigabyte version, do that!
Regardless of whatever you get, those are the two parts you'll need to upgrade first. Your CPU and mobo might even be good for a large portion of the next generation.
Edit: No you should never have stopped PC gaming. Now is when it's getting really damn interesting. More ports are coming to PC now than in the entire generation and with similar architectures for Xbox and PS4 to PC, expect a lot more.
Edit 2: Forgive my ramblings I'm quite delirious at the moment due to fatigue.