too many mags vs. a reasonable number
If you are looking for some reasonable method to determine 'how many mags is enough?' here's one opinion: for me if it's a semi auto high cap 'assault style' rifle I look at what the military (whose ever it may be) carry with that rifle. In the case of the AR15/M16 platform a typical load carried by our service men would be a mag in the rifle and 6 in pouches, usually two pouches with 3 mags each, so 7 mags is a good start. For AK47's there are different 'typical' mag carriers depending on the country, but something between 5 and 7 mags is pretty normal. M14/FN FAL/HK 91 or other 7.62x51 rifles usually carry 6 + 1 mags, but they are 20 rounders, so 120 rounds. The weight of 120 rounds of 7.62x51 is similar to 210 rounds of 5.56 apparently. For handguns it's usually something like 2 or 3 mags, the idea being that if you are going to carry additional rounds you are better off with more rifle rounds than pistol rounds. Plus, if you have been through 20-30 rounds of .45 ACP and the fight's not over you obviously have a larger problem on your hands.
The reality in the current political climate is that "you can't have too many magazines" really means "you can't have too many high capacity magazines" with the assumption that they will become very difficult to obtain. You might as well buy more than you ever think you would need if you have the money. You will always be able to sell them to your friends if you decide you don't need them later.
As far as 'do they ever wear out?' yes, but unlikely unless you are shooting competition or you just practice an awful lot. Most of the well made magazines will last for thousands of rounds. FYI while stainless is easier to take care of in most cases, the reality is that silicone chrome springs don't develop "memory" while the stainless mag springs may.
As far as brands, AVOID the U.S.A brand mags. They suck. I'm not a big fan of Triple K or most other wide distribution after market mags either. Generally for pistol mags I would say to buy the factory mag or possibly Scherer mags for Glocks or MecGar mags for pretty much anything else. MecGar makes most of the OEM magazines anyway, so while they are technically "aftermarket" they really aren't.
For AR15 mags stick with either military contractor mags or Magpul Pmags. The Magpul followers are probaby worth the money as a replacement to the original military follower, especially if the follower is one of the old black ones. The green military followers are pretty good.
For other military semi-autos try to stick with the military mags as well. AK mags are their own subculture, there is a pretty wide range of quality depending on the country, luckily almost all of them work.
Last bit of advice, keep your mags clean. It doesn't take much crud in a mag to bind up the follower. Clean your mags when you clean your guns.
If you are looking for some reasonable method to determine 'how many mags is enough?' here's one opinion: for me if it's a semi auto high cap 'assault style' rifle I look at what the military (whose ever it may be) carry with that rifle. In the case of the AR15/M16 platform a typical load carried by our service men would be a mag in the rifle and 6 in pouches, usually two pouches with 3 mags each, so 7 mags is a good start. For AK47's there are different 'typical' mag carriers depending on the country, but something between 5 and 7 mags is pretty normal. M14/FN FAL/HK 91 or other 7.62x51 rifles usually carry 6 + 1 mags, but they are 20 rounders, so 120 rounds. The weight of 120 rounds of 7.62x51 is similar to 210 rounds of 5.56 apparently. For handguns it's usually something like 2 or 3 mags, the idea being that if you are going to carry additional rounds you are better off with more rifle rounds than pistol rounds. Plus, if you have been through 20-30 rounds of .45 ACP and the fight's not over you obviously have a larger problem on your hands.
The reality in the current political climate is that "you can't have too many magazines" really means "you can't have too many high capacity magazines" with the assumption that they will become very difficult to obtain. You might as well buy more than you ever think you would need if you have the money. You will always be able to sell them to your friends if you decide you don't need them later.
As far as 'do they ever wear out?' yes, but unlikely unless you are shooting competition or you just practice an awful lot. Most of the well made magazines will last for thousands of rounds. FYI while stainless is easier to take care of in most cases, the reality is that silicone chrome springs don't develop "memory" while the stainless mag springs may.
As far as brands, AVOID the U.S.A brand mags. They suck. I'm not a big fan of Triple K or most other wide distribution after market mags either. Generally for pistol mags I would say to buy the factory mag or possibly Scherer mags for Glocks or MecGar mags for pretty much anything else. MecGar makes most of the OEM magazines anyway, so while they are technically "aftermarket" they really aren't.
For AR15 mags stick with either military contractor mags or Magpul Pmags. The Magpul followers are probaby worth the money as a replacement to the original military follower, especially if the follower is one of the old black ones. The green military followers are pretty good.
For other military semi-autos try to stick with the military mags as well. AK mags are their own subculture, there is a pretty wide range of quality depending on the country, luckily almost all of them work.
Last bit of advice, keep your mags clean. It doesn't take much crud in a mag to bind up the follower. Clean your mags when you clean your guns.
I'm not saying what the gun is or where the mag source is until I already have the gun and like 30-50 mags because I don't want anyone else taking them. 
