How long should high quality speakers last?

My uncle has a pair of ADS 1290  that still look and sound good.   Have to be over 40 years old. 

At around the 25 year mark, I started to hear a noise from one of my Von Schweikert VR-4 speakers.  It sounded like it was coming from a tweeter. I checked and the original tweeters were no longer available (I later found some NOS tweeters on eBay). I checked with Madisound and selected a pair of ScanSpeak tweeters.  Installed them and still had the problem. Turns out it was the midrange driver (go figure). An Audax driver that was still in production.  Replaced them and all is good. 

I actually prefer the ScanSpeak tweeters, so I left them in.  These speakers are sitting under covers waiting for my son to have space. 

I'm rocking a 35+ year old pair of KEF 103.2s (butyl surrounds). The previous owner replaced several of the caps in the crossover because they were leaking. So far, so good (they sound fantastic).

My ADS L1590 speakers were purchased new by me in 1984. They still sound wonderful. Unfortunately they haven’t gotten any smaller over the years. About 100 lbs. each. :-(

I also have some small Boston Accoustics speakers from the 90s (one pair was second hand). They still sound fine.

My guess is that aside from abuse it’s the environment that has the biggest impact on longevity. High humidity, temperature extremes, and physical impacts, small children, and so forth probably degrade the drivers and crossovers more than just time and use.

After owning Revel Studios (a very highly regarded loudspeaker in the early 2000s) for more than 20 years, I decided it was time to replace them even though they still worked as well, I think, as when they were new. So, why?

Comparing my Studios with several current state of the art speakers (and employing equipment/cables as similar to what I own as possible), it quickly became apparent to me that 20 years of speaker technology developments had wrought some real improvements in sound reproduction. 

Accordingly, I now own Magico A5 and am enjoying vastly improved clarity, soundstaging, and imaging.