A good monitor will probably still be good in 5 or 10 years. Not so for a top-end video card.
EDIT: To provide some specifics, my gaming PC is a Phenom II X6 1090T 3.2GHz with 8GB RAM and a GTX460. The "Windows Experience Index" is 6.9. That is basically two or three generations out-of-date. However, it plays MWO very well.
I am a little tempted to upgrade but honestly I think a good joystick or other kind of game controller would be more of an addition to my gaming experience than a better video card, CPU, whatever. There are plenty of ways to spend money on your gaming PC without actually spending it on the PC.

Edited by jeffsw6, 16 March 2013 - 02:04 PM.