How long do speakers last?

I have a pair of Polk Audio Monitor 10's that I bought brand new in 1987 that are in mint condition and sound like they did the day I first hooked them up.

Possible, but not probable. If there are electrolytics in them, they need to be recapped. Replacing mylar caps will increase transparency.

Plus, NO speaker I ever bought sounded like the day I bought them after a play in.

@allenf1963 I had those years ago. There were great speakers for the time. They killed Advent and ARs and the like, Just don't let them sit for long periods of time. The mid drivers tend to freeze up.

I think in depends on the condition, restoring, parts availability, and bang for your buck. My last project refurbished late model IRS Betas, was time consuming and certainly not cheap. The all in cost has me smiling as that I’m sure is a fraction of the outlay for ‘comparable’ new. 

There are far too many variable involved that there is no meaningful answer to how long to expect speakers to last.  I've heard drivers that are really old that have held up well, even without a re-coning.  That is particularly the case with woofers with the pleated fabric or paper surrounds.  It is far more common to see crumbling on soft rubber surrounds.  Many modern speakers with such surrounds go bad in 10-15 years, while I've hear old pleated paper drivers that are 70 or more years in age. 

The midrange in my system (compression driver feeding a horn) is at least 80 years old and it works fine.