Well, this is certainly a "spirited" discussion, so here's my $0.02! Spiders take a long time to break in and constantly are changing. While the majority of the break in occurs in the first hours, the fibers continue to fatigue and break; to what degree is another discussion. There is also a"Stability of Shape" which measures a spiders deformation over a long period (think subwoofer mounted with the axis vertical and the moving mass of 250 grams). Spiders also change drastically with changes in temperature, humidity, and excursion. The last is not widely known but large excursions "untangle" the fibers. Upon rest, the fibers sort of re-entangle (is that a word?). And to confuse it more, there's cotton, acyrlic, polyether-cotton, bimax, bimax sandwich, conex, nomex and others all reacting differently to temp, moisture, shape stability, etc.
A typically spider cost about $0.09; this means spiders are a commodity. And commodities leave no profit left for R&D. A "cheap" but good spider tester is $10k (True Technologies). Dr. Kurt Muller has done a little testing but all static hysteresis. Wolgang Klippel et al have done quite a bit but their instumentation starts at $30k or so. There is a need for research and our company, DYNE Analytics, is considering submitting a research paper for ALMA International's WInter Symposium in 2013; all we need is a lot of time and a lot of money!
So, I guess I am saying that spiders change in the short run (a single large excursion) and the long run.