No.
Keeping 70+ magazines loaded seems unnecessary.
I do keep 5 or 6 loaded: often for years.
Rastoff, you are worrying about nothing. Do your car or truck springs compress with time? Can you imagine if you had to replace your truck springs every so often because they have sagged, or had to keep your car on stands to take the load off the springs when not in use? Nonsense. Springs are designed with a hefty safety margin, trust me I know, I am a mechanical Engineer, I had designed more springs in my working life then most people had hot breakfast so, keep your magazines loaded especially if your gun is for self defense.This is almost right. Keeping a spring compressed will have an affect on it. That affect just won't be significant.
If it had no affect, the mag wouldn't get easier to load, would it?
I am currently doing a test on this very subject. Last year in June, I compressed a spring. It has been sitting compressed every since. In June of this year I will release it and see how much it lost, if anything.
I have a comfortable chair that is around 30yrs old. As the years went by I've found I'm sitting lower than originally.It is getting considerably harder to get out of the chair each day.The springs have weakened significantly.
To put it in gun terms the chair has caused my butt numerous FTE's from the chair.
As far as the springs in our mags go the opinion definitely seems to lean on the side of having no affect.