How long does it take a decent quality speaker to "wear out"?

On my circa 1982 AR-9, the smaller sheets of diffraction limiting flat acoustic panels around the tweeters and midrange drivers turned to a messy dust and need to be replaced. (These are panel around the drivers that fit inside a larger, thicker acoustic foam that has not deteriorated), not the "surrounds" that are attached to the drivers). Fortunately, I think I've found some materials that are similar and self-adhesive and will use those. Looking forward to getting another 10 to 30 years use out of these babies before I kick the bucket and they get passed on to my nephew or they end up in a yard sale for $50...Sadly, I could see that happening. 

Yes, modern speakers should sound "better" but to tell the truth, I LOVE my old AR-9.  I would only consider replacing them with something similar like the Arendal 1723 THX or maybe the lower end Polk R700 depending on my budget and 401K in this inflationary, regressive economy. 

Maybe 'wear out' is the wrong word.  I don't think speakers are like jeans.  Jeans wear out from use. I think the fatigue life of most of the parts of a speaker are going to be vanishingly high. You could probably play most speakers 24/7 at moderate volume or a decade or more. This is not true if you play them at super high volumes. 

How long does it take a speaker to degrade is perhaps more accurate. Environmental considerations like pollutants and ozone in the home might cause plastics and organic materials to degrade. I suppose it depends on the environment. Oil filled parts may dry out.  

I will let you know when I wear out a pair.