How often do you replace the springs on your kick pedals? Is it by time elapsed, when they start to feel sloppy, or any other factors? If you're a double kick player, do you find the dominantly used pedal getting sloppier before the secondary?
Always have a spare spring in your stick bag's pocket, and better still, if you have a backup pedal, keep it nearby on stage with you during a performance. Thus never really having to worry about it. Otherwise, it depends on how much tension, and use, the pedal gets.
Knock on drums, I've never had to change a spring. I have had other parts of a pedal go bad - the leather strap on my old Rogers broke; threads have stripped out on an old pedal and on a new Yamaha direct drive, and I even broke the beater shaft on an old pedal I can longer recall the make of. The springs have been fine, though.