The computer I use now does alright WoW, I mostly run it on good or high unless I'm in a very crowded area. That said, I'd love to be able to max out settings and enjoy the new graphical updates for MoP, so I've been looking to upgrade.

This is my setup atm (a pre-build setup I bought like 2 years ago):

CPU: AMD Phenom(tm) 9650 Quad-Core Processor (4 CPUs), ~2.3GHz
4096MB RAM
MB: Gigabyte GA-MA770-UD3
GPU: NVIDIA GeForce 9800 GT
1680"x1050 22" screen.

What should I be looking to upgrade to increase my performance? Should I just get a new setup altogether? I don't have too much money to throw around, and I really only play wow on the computer, so I'd like to keep that as the goal.

If you need any more info let me know, thanks.