It's almost impossible for a spring to weaken from use. The only way I can think of, is if metal is removed, like by abrasion or extreme corrosion. If the metal is not removed, then the spring constant will stay the same because the inherent stiffness of the steel (Young's Modulus) is for all practical purposes a constant. You can't change it by heat-treating, and only a tiny bit by alloying, and definitely not by just springing it a large number of times.

Fatigue will cause a spring to break eventually, and there can be a brief period where the spring is partially cracked but not "in two" yet, where it will feel weaker. But once a crack starts in a spring, it usually breaks off very soon after.

Most reports of steel "going soft" from use are pure bunk. A spring might seem weaker if the friction in the pivot has increased, to where the spring has more force to overcome to spring back. But that's not the spring's fault.

I look forward to your results, interesting project.