IMO if you have an expensive double, then by all means get snap caps and baby your gun. if you dont have snap caps you can make them from empty hulls: pull the primer, and fill the primer pocket with polyurethane. let it dry. trim it flush.
pumps are a different story: there are 870s and mossberg 500s out there that have been dry-fired thousands of times, and stored for years while cocked, and never have any problems.
on your run of the mill pump - worst case, a replacement firing pin is $15. springs are a couple bucks.
there are 870s that have been in use and abused by mil/LE since the 50s and 60s and are still going strong, i doubt storing them in your cabinet is going to hurt them regardless of how you do it.