I don't see the point in upgrading and would spend the money on a better card and Nvidia's Kepler should be out soon or go with AMD's 7k series radeons. The older i7's are still very strong and I use my PC for pretty much the same thing with some encoding every once in a while. My board however is a good 5 years old; basically my system does everything that I need it to do and I am personally waiting for what Ivy, trinity APU and PD before I upgrade off my current board.
As the other person above me said, SSD. Within a 6 month span last year I upgraded to a 570GTX, Phenom II (from a old A64 x2) and my Intel 320 series SSD. i will say that my best upgrade out of those would be my SSD
Basically it felt like a brand new system. It won't help your FPS but makes those loading screens go by in a flash.
For SSD's I would recommend the Crucial m4, Samsung 830, or the Corsair Performance proEdited by Agent_kenshin - 2/14/12 at 11:08pm