longevity of good speakers

"The fluid in tweeters may dry out" -

or midrange (my Hyperions have ferrofluid damping in 6 1/2" midrange).

I believe fluid can be replaced.

Speaker electrical characteristics change as the drivers are heated.
Maybe a heated speaker....say running 50% of 'redline' for an hour or so may be even easier to damage.
Caps in crossovers also deteriorate with age. Letting them just sit in a closet is probably worse than running them daily, if not electrically abused in the process.

That reminds me,shipping speakers by air can cause the ferrofluid to leak,from the pressure change.

A properly designed speaker should last a lifetime with a little maintenance.

Vintage speakers were made a lot better and will last a lifetime....I love my sansui sp-5500 horn speakers with cryoed inside wires and all crossover parts cryoed!..Now all I need to do is put some of Alan Maher's CBF crystals on the crossover parts. Someone over on the audio asylum forum said these crystals works great inside the shells of a ac plugs and ac IEC connectors. He said it improved audio and video A LOT!...They now sell the crystals in bulk by the pound!