I have only been shooting Orlite mags - probably due to the fact that I own about 15 of them and nothing else.  They seem to give me good service but in the long term should I be stocking up on USGI or some similar type of metal mags.  I don't want to get 20 years down the road and have the feed lips or bolt stop wear out on these and then find there are no more 30 rounds left under $200.

I have a stack of the Orlites.  They work just fine in my rifle, but I assume they will not last forever.  If you are worried about future supply, you can always buy a stack of Orlites and stick them in storage, and forget you have them.

At $10 each, you would need to wear out three Orlites for each good USGI.   The USGIs are better, but I doubt they will last three times longer.