What are the specs of your PC? I would say get a decent 22nm videocard at the end of this year over anything else if the rest of your rig supports it. I'm waiting for true Nvidia Maxwell cards to come out myself.
If a full upgrade is required I would suggest a PS4 instead. It has much better price/performance than a full PC upgrade but won't perform quite as well. You also get ND games, which are worth the price of admission alone.
I'm actually not sure what the specs are, tbh. It has never struggled to run anything, but I also haven't pushed it and it's about 4 years old. I had a local shop custom build it for me, and at the time it was about 80% of the way to a monster machine. The graphics card is the most annoying part - it's an ATI and has a weird quirk where it "under-heats"... if it's not running 3D graphics and the room is cold (which is an issue here in Canada) it will trip out. I've always kind of regretted the machine because I didn't go all-out like I wanted to because of low funds and a cranky girlfriend. Neither are an issue now so I kind of think it would be fun to go all out on a PC.
A PS4 also is intriguing, however. I do enjoy a classic console and I have a feeling a lot of friends will have one, making it easy to play some COD online with them. I'm hopeful that some PS3 titles that I missed will be available through download or cloud. The early performance results on the system so far sure are solid.
When are the Maxwell cards expected to release?