actually the plain steel (zinc plated) spokes usually are stronger (more tensile strength) than comparable stainless spokes...but after they have corroded and rusted, that may not apply.
I used to subscribe to the "wit and wisdom" of Jobst Brandt, who tells us that a spoke is a working part of a moving system, and that they are subject to wear and fatigue cycles...etc., etc.
But these days I'm less of a true believer and will re-use good (and good quality) spokes for my own wheels.
So far, so good.