How long should high quality speakers last?

YMMV but I purchased a pair of ADS L810 series2 in 1978. Used them sparingly until about 6 or 7 years ago and passed them down to my little brother. He is still enjoying them today. They have survived many moves but still play like new. All original parts.

Of course, all of these are anecdotal and speaker design, quality and your luck will determine how it turns out.

@unreceivedogma wrote:

Did I say “sound the same as new”? 

I did not. 

However, I obviously would not still be using them if I was not getting anything less than outstanding performance from them. 

It appears the post you were replying to has been deleted, but nonetheless I'd say you would definitely be in your right to claim your vintage speakers sound "like new," also being they have been serviced regularly. Who really, from actual experience, refers to and knows about the sonic difference between more or less brand new, properly run in Altec's and their decades old, well-kept equivalent? Demagnetization of Alnico magnets in particular, as has been touched upon, is really only an issue with excessive heating of the magnet from large voice coils or shock treatment, and any natural degradation of magnets is hardly anything other than academic in nature.

The real takeaway here is that such drivers, even decades old, are so transiently alive, dynamic and natural sounding that many newer, lower efficiency modern drivers seem stale and lifeless by comparison. Speaking of sonic detrimements due to aging here misses not only its relevance but also fails to take into consideration an unbiased assessment of these older designs and their merits.

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).