longevity of good speakers

i am somewhat new at the audiophile game and i am looking for some advice on speakers. NOT SUGGESTIONS. my question is in buying a high caliber speaker like the verity ovations on the used market, with average play, approx. 20 hrs./week, how long can they be expected to play at their top form? in other words, if i buy a six year old set of good speakers, how long could i realistically expect them to give me great satisfaction?
The fluid in tweeters may dry out after about 15-20 years. Woofers can last longer - 30 years or so. It all depends on the quality. Of course one hour of serious abuse can ruin a speaker at any time.
I've never heard of a hour time limit or rating for speakers. The foam edge surround style deteriorate over time(you could get them refoamed),but the rubber surrounds seem to keep on going.Some broadcast stations run their monitors,24/7.
"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!
I have a pair 25 year old Wharfedale Diamonds. I had to do a little glue repair on the dust caps. The tweeters look like ones you could replace for $6 bucks- for the pair! No one can believe how good they sound.
Foam deteriorates, some people replace caps, but old cared for speakers should last a long long time.
I need to get some of those magic crystals for sure!!And a smart clock and a few call-in tweeks and some stones and a few of those twisted tuning forks,etc.
I forgot to mention I keep all of my speakers in special pyramid structures with crystals hanging inside.
One of my pairs of speakers is 30yrs old and sounds wonderful. The other is 13-14yrs old and sounds wonderful too.
I can beat 30 years. My mother still uses my first set of speakers, I bought second hand in about 1970. They are Leak mini sandwiches and still sound pretty good, a bit soft of course. She is nearly deaf anyway, so that's alright.
One of my pairs of speakers is Celestion SL 700s from the 1980s. The Zu website claims a life expectancy for their Essence speakers of "Lifetime on cabinet, 40 years plus on Zu260FRD/G4, 15 years on ribbon foil (serviceable)" and for their new Soul Superfly speakers of "100 years plus cabinet, and drivers, including the Zu260FRD/G4 HO; even in direct sunlight."
Ive got original Altecs from the early 60s working great. Pair of RCA from 1950s again fine condition.
I think you might want to run this question by Bill Legall from Millersound;he is a very highly respected speaker repair person and he can probally give you some good advice as well.Here is his contact info.
1422 Taylor Road
Lansdale, PA 19446-1531
(215) 412-7700