My understanding of springs has always been that the spring rate stays contstant throughout the life of the spring, but all that "wear" really affects is the spring height. So the springs don't really wear out, per se. They will just ride lower...
95 LX/SE V6 5 Speed NUN 1 http://www.cardomain.com/memberpage/588083
"The Contour SE is the best American car I have ever driven and one of the best cars period." Larry Griffin - C&D