Spring material is the key there. The reliability problems we had with the M9 Magazines from about 2000 to late 2005 was attributed supposedly to the improper finishing on the inside of the magazine itself. However I disagree with the DOD's assessment of it having spent thousands of hours in weapon repair. It was terrible checkmate spring material, as these things even when polished and "fixed" according to specifications would fail from the first loading. As in the spring stopped working. Bends, kinks were the normal procedure. What this means is to test the magazines out for your chosen weapon. Use magazines that have a good reputation for reliability. Some will run for decades as has been noted, and some will wear out shortly.
Battle rifle magazines however I have seen fail more in the feed lip area. M1911 magazines tend to fail from rust and corrosion on the inside especially military style non tear down sorts.
I expect to have to replace springs or magazines regardless of what I carry or decide my life depends on.
For pistols however or when I was overseas every time I stripped the weapon down to clean it, I would swap a magazine. This was roughly once a week for a full strip. 7 M16 magazines meant every 7 weeks one was rotated out. This allowed me to clean the magazine and check it over for cracks and wear and tear on the springs. Currently Once a week or every two weeks I swap a loaded pistol magazine out for a unloaded one. Same principal applies. Check it over, and if there is a question on spring tension it is thrown out on the spot, or put in to a bin for replacement parts.
However I think that downloading a magazine to save spring life is harder on the magazine spring than fully loaded, but that is unverified scientifically. Just my observations on what I have seen in the years of a direct support repairman or Armorer.