Don't forget that magazines are expendable items that will wear over time (if you use them). When you inspect your magazines and find one damaged (e.g. cracked or spread feed lips, etc.), throw it away and get a new one.
This is hard to embrace for some of us who lived through the magazine restricions imposed by the Omnibus Crime Act of 1994 (aka the assault weapons ban). In some cases, we believed that our magazines could not be replaced, so we had to nurse them along indefinitely. I believe that almost all of the AR mags I acquired up to 2004 were used when I got them, and some because garbage during use over that time.
Naturally we may face similar or worse laws in the future, but that's why you should plan now. If you use your magazines, you will wear some of them out. Prepare now for that eventuality.
Oh, and more is always better than less. Unless you're trying to swim.
If they are "banned"............ Well, we are in trouble anyway. Guess then I'll make do with 10 rounders, although everyone should realize they can be banned as well.
SHTF? If things get really, really bad, you are not gonna shoot your way out of it, no matter what you daydream about. No food, no medicine............ No magazines are going to replace those. And the "bad guys" are probably going to be just as heavily armed as you are.
Just my opinion.