Until about two years ago, I always added EQ. Then I upgraded my playback system, and suddenly many older recordings that I had messed with sounded terrible. That's why I stopped doing it.
Bingo! If you have a cheesy setup, then let 'em alone. I have the option to mess around with mine, and I do, but I do multi-channel recording and I master using:
MOTU 2408mk3 > QSC RMX2450 > Earthworks Sigma 6.2 monitors
If you don't have the right setup, what you think you're changing you're probably not. You're compensating for room and equipment instead of for the recording. Then when it gets played elsewhere it sounds very different. I have not found this to be the case with stuff I've worked on using the setup listed above.
Wayne