How long do good speakers last?

Talk about "vintage"?  I am still enjoying my AR-2ax speakers from 1969!  The original ten inch woofers utilized rubber surrounds that have never needed replacement. 

I did have to replace one of the mid range drivers after about ten years - the corroded level controls in the 1980's,  and a burnt out dome tweeter just last year.  Fortunately, Parts Express carries a substitute AR dome tweeter for about $20 that matches the original perfectly.

These speakers still sound as sweet and natural as ever - especially with the latest improvements in analogue and digital sound sources!

As long as the spider and surround is good so are the woofers which take the most beating. I have witnessed all paper cone woofers last 35 years in a Leslie organ speakers. The HF longer. Mid and high frequency depends  on componenent material used and engineering design.

I had ac pair of JBL Laners go 20yrs before the woofer foam started to go bad

I've got a  pair of 1959 JBL Hartsfield the 15inch woofer is still in good shape after all these years.
In year 2000 I bought a pair of Klipschorn the 15 inch and horn driver are still in good shape.
In April this year I purchase my 3rd collection of JBL Everest DD66000 used by the last owner  who had them since 2009.
I prefer  drivers are made of cloth treated surround it will last for Donkey's years.
I had many other pairs of speaker with Form surround they last 3 to 5 years in Tropical Singapore.
So I only purchase the once with cloth treated surround. I am very happy of my purchase of my three pairs of speakers in my collection and I do know they will out last me. at age 67 years.

Depends on the speaker mostly, and how much the cone moves.
If you your speakers have "long throw" woofers with excessive cone movement, re-foaming them will be a regular activity for you.

If on the other hand you own a pair of K-horns like myself, there won't be any need to re-foam because the cone never moves more than a 1/16th of an inch, worst case scenario. No movement, no wear! 

I bought my speakers new in 1978, the access panel for the woofers have never been removed. Bass is as good as it was new...