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?
128x128mpmll
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.