I used to service all the Glocks for my local Sheriffs department and I can tell you that mags left fully loaded will weaken the springs quite a bit over time.
It's best to change mag springs in a mag kept loaded once a year, every two at the most.
They are not that expensive, you just have to ask what your life is worth.
If you know a LEO armor who can order mag springs for you with you being able to pay for them, Glock sells them dirt cheap to department armors.
Many gunsmiths are certified Glock armors, as I was, they may be able to save you $$$ and I got them very cheap. I'm sure they will mark them up a little, but if their honest, they will still cost little.
Glock, if your reading this, I'm retired.