I remember from one of your other threads that Glocks are crazy expensive in Guatemala, but I don't have a clue what that means for magazine prices there. You mentioned nice gun shops being 6 hours from you. Can you order them online? Is that legal?
There's considerable (and heated) debate over whether mag springs are worn out by: (a) loading and unloading; or (b) simply leaving them loaded. I'll leave that debate to folks who know considerably more about the technical side of springs than I. That said, I've never worn out a magazine myself. I did rebuild 5 that I bought used, but that's as close as I've come. Just bought new springs and followers and popped 'em in.
For a defensive pistol, I like to have ~10 magazines. If I came across a great deal on them, I might want more. I don't carry more than 1 spare at a time, but having a bunch of magazines means that I can load them at home. Since most of my local ranges charge by the hour, I don't want to waste my time at the range loading magazines. If I'm at the one that charges by the day, it's less of a concern.
If it's just a target pistol, I'm good with having 3-5 magazines. Most of the time that I shoot those, it's at the "charge by the day" range, and I can load mags while Mrs. McGee shoots. (If I go to the range alone, I usually just take my defensive pistols and practice with those.)