How long do high quality speakers "last"

If one treasures cabinetry this is also an area to be aware of, as veneers, if not properly glued/pressed, can detach from the particle board (or the more rarely used plywood) over the gears, as can joints, and solid wood, if not properly dried, can "work" itself to create cracks or otherwise bend out of shape. Cross-over parts such as electrolytic capacitors dry out after some years. As already mentioned different surround materials deteriorate over years, some more rapidly than others, also depending on atmospheric conditions such as humidity and shift in temperatures, and direct sunlight is never a friend of most any driver. It seems treated cloth surrounds lasts for decades, and where used in horns and hidden away are often regarded as mint-condition young drivers even after 25 years. True heirloom speakers that combine excellent cabinetry and overall craftsmanship with quality drivers and cross-over components, and that are used carefully under "normal" conditions,   should last many decades without sound degradation, as I'm sure quality speakers that do not aspire to "heirloom"-status should easily last 25 years or more, if properly treated. 

Quality speakers are made to quality standards and can last for decades.

I have a pristine pair of ADS L-520's that I bought new in 1980.  They are currently used in a secondary system.  They have been well taken care of, not exposed to temperatures extremes, driven with only quality electronics and their woofers use butyl rubber surrounds that will last forever.  So I see no reason that I can't get another 36 years out of them.

Wondering if the OP will see this and chime in on the condition of his Response 2's now that they are roughly 22 years old.  

I have a pair of Kef C55 that were purchase about 1990 that still sound fantastic. They have taken quite a beating, too.

I expect my Silverline Preludes to really last as they have magnesium/aluminum drivers and rubber surrounds. The crossover caps may die before the drivers, but I’ll likely get bored and replace the speakers with something else due to boredom or curiosity well before any of that. Note that I use my trusty old Boston Acoustics A60IIs in my TV system and have replaced the woofers once (foam degradation). years ago…they still kick a--, so to speak (from 1988 or something?). I assume the ferrofluid will dry up eventually in the tweeters but so far they work fine.