I do brake fluid every time for pads. I just flush a bottle thru the system. Water & rust are really "bad" for a system, and the fluid is only a few bucks, so I splurge...
Heck, on my Cobra brakes Mustang, I change fluid before EVERY event. Which is somtimes like more than oncec/month!
As for all the other fluids. I change EVERYTHING (and I mean EVERYTHING) at 60K miles. Oil, tranny fluid, brake fluid/pads, rear dope, radiator fluid, serpentine belt, battery... I figure once its done, I got another 60K miles on it. THen at 120K I decide to do it again, or sell the car (Michigan 10 year old rusted car).