How long should high quality speakers last?

I have a single Stephens P-52 woofer with a P-15 horn driver in a late 1940s Stephens cabinet.  Still works well, and is still seeking a companion to make stereo.  Otherwise, in no particular order and still working.....I have JBL C37 (D130 + 075 tweeter), 1950s, Altec 604-8G, 1970s,  Dynaco A-25, 1960s, ADS 400 and 810, 1970s, (400 was refoamed, 810 are butyl), Magnepan 3.6R, early 2000s.  It appears that speakers last a good while.  Crossovers that use electrolytic caps should be updated.  

I have a single Stephens P-52 woofer with a P-15 horn driver in a late 1940s Stephens cabinet.  Still works well, and is still seeking a companion to make stereo.  Otherwise, in no particular order and still working.....I have JBL C37 (D130 + 075 tweeter), 1950s, Altec 604-8G, 1970s,  Dynaco A-25, 1960s, ADS 400 and 810, 1970s, (400 was refoamed, 810 are butyl), Magnepan 3.6R, early 2000s.  It appears that speakers last a good while.  Crossovers that use electrolytic caps should be updated.  

The serial numbers on my Altec 604Cs and on my 604Ds are 1956 and 1958 respectively. I have had them for 45 years.

I rotate them once a year, and have them serviced every 15 years.

The crossovers are Mastering Lab. The caps have been replaced. 

@mkaiser 

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. 

The rest of your statement makes no sense to me.