Most important purchases for upgrade.
Monitor, Keyboard, Mouse and speakers.
these will not change no matter how often you flip your CPUs and GPUs. And since this is your primary means on interacting with a PC, is more important than CPU choice IMHO.
(So far my 1920x1200 monitor has lasted 4 years, and thats a LOT of hardware flips maybe a dozen CPUs and a half dozen mobos? )
So true, I remember when I kept going on a really old monitor and crappy speakers and keyboard because I never would set aside cash for it. I always used to put everything into what goes into the tower.