Some discussions are hard to stay out of. In 1961 or so, I got into a discussions of springs and durability with my metallurgy prof at UFla. His comment was, "If it takes a set, it's not a spring." Meaning, of course, it was less than high-grade quality.
Maybe I've just been lucky, whether it's my 220,000-mile Toyota 4WD having no loss in ride-height, or (in younger daze) my race-motors' valve trains with no failures.
In fact, one of my most reliable-feed .45ACP magazines has a spring which is noticably soft--it's a home-made 8-rounder. Go figure.
Anyhow, from a metallurgical standpoint, any spring from a reputable source should never take a set nor weaken. (Caveat: Beware the lowest-bidder problem!) Noticeable degradation should take hundreds of thousands of cycles of use.