Self confessed magazine hoarder, having lived through the Clinton ban, and fearing another from the brain trust in DC.
Post ban, I got the 20s we'd had in the service, NHMTGs. As the 30s became prevalent, got some of those. Maybe a half dozen 20s were kept loaded with 55 gr, and another half dozen 30s with green tips. Been shooting those up lately, after more than 20 years storage; they worked fine.
I had an MSAR AUG with its poly mags; some stayed loaded for years, and worked fine.
Swapped that on a real AUG, but the NATO version, rather than stockpiling two kinds of magazines, which led me to trying MagPuls...thus far, they have been great, and it's time to believe in plastics. The AUG has a poly firing package; only the springs are steel, and it is reputed to be very durable. An Aussie training film shows the troops cleaning it with water in a stream...
Now, OTOH, have had a Scorpion with its 1st gen translucent magazines, and some of those have developed feed lip cracks. The problem was attributed to solvents and oils. It's not an uncommon problem, and the factory has redesigned the mags of a different material; MagPul makes some too...both have a great reputation.
I guess it just depends.
It does seem prudent to keep those half dozen mags loaded, though. Just because.
Moon