I put 7,500 - 10,000 rounds a year thru my primary 12ga shotguns - and I change the firing pins and springs about every 3 years.
You can definitely wear out the springs and firing pins in a shotgun - check the point of the firing pins for any flaking / pitting - Browning's firing pins seem to have been a problem for the last 5 or 6 years - showing signs of wear at about 5,000 - 7,500 rounds on various over-unders and on a variety of gagues. Replacing them with titanium firing pins lengthens the life of the pins.
Taking the stock off a shotgun - at least twice a year - to clean and inspect the trigger group, springs, firing pins etc is routine maintenance, and maybe more often, if you are hunting or shooting on real wet days or if you store your guns where you may get a little condensation. A lot of guys have been dissapointed to find a significant amount of rust and corrosion inside their stocks because they weren't taking them off periodically.