spring life
as a person that works for a spring manufacturer, I believe that I can shed light on the issue of spring life. springs wear out through the repeated compression-relaxation cycles. store them empty if that is what you want (cant imagine why) store them full so that they are ready to use when needed.
springs are manufactured with special steel wire then heat treated to maintain its shape. this allows a spring to be compressed and then for it to return to its original shape.
unless misused or cycled hundreds of thousands of times, the spring will perform as designed.
the issue people should be concerned with is not spring life but whether or not you have the right spring for the job. springs have different rates of compression and are designed by the mfg. for specific tasks. as an example, I have an EAA pistol in 10 mm, I use a 22 pound spring in the slide to control recoil, when I change the barrel to shoot 40 cal, I change the spring to an 18 pound rate. I use the same magazine springs for both.
hope this info helps explain some questions.