Buy a pair of ten year old $40,000 speakers for $4,000 or new ones at that price point?

Here is my take on this.  The $40,000 speakers.  Have you heard them?  Do they sound better or worse than the $2000.00 speakers?  Never buy something sight unseen or unheard.  Also,
an important thing.  The drivers used on the $40,000 pair of speakers;  Can the woofers be
re-coned with the same material or if the surround is cracked or torn match the material?  Can you get replacement diaphragms for the tweeters?  If the mid-range unit is metal can you get replacement parts.(Voice Coils)   Unless all of the drivers are paper edge surround expect after about ten years that rubber surround dry out and foam surrounds rot.  Some tweeters have dampening behind the titanium / beryllium which can rot over time.  My point is that a new pair will be good for at least ten years and affordable to repair.  How long will the $40,000 now $2,000 pair last?  And can they even be rebuilt at a reasonable cost?

Typical cost on good used high end speakers is going to be much closer to 33% of original list - anything below that and you have to ask why.

I got a pair of B&W 802 Series 80 floor standing speakers from 1981 for nothing from a woman who was downsizing to move into a smaller apartment. She paid approx. $4,000 in 1981 for them, which in today’s dollars is closer to $10,000.
The dealer upgraded the midrange/tweeter heads so they’re technically Model F’s.
She drove them with an underpowered integrated amp with 12 gauge speaker wire in the 35 years she owned them. Knowing that the caps needed to be upgraded, I sent the crossovers to Walt D’Ascenzo, a brilliant audiophile who solved a ringing issue for Dave Wilson of Wilson Audio and shared tips with Walt Jung, the legendary audio engineer. What he sent back improved the 802’s to a much greater quality than they were originally. I’ve heard the latest offerings by B&W and have been underwhelmed. As a side note, with every tweak I make with better interconnects, power cords, and power conditioning, the speakers sound more fantastic. So when considering old speakers, don’t throw the baby out with the bathwater.

mcmanus, I would look for new speakers at $4,000.00 rather than used upmarket speakers.  There are a number of reasons for this.  First is warranty.  There will always be a warranty with new speakers.  Even if you get a 'warranty' from a dealer on the second hand speakers it will likely be only a few months.  Second is technology.  There have been a lot of advances  over the past decade, and there continue to be.  Driver materials in particular are always improving.  What was top dog ten years ago is not top dog now.  Third reason is wear.  Moving parts wear and there is not much getting round that.  Time will also ravage the finish on products.  A possible fourth reason is design.  This won't apply to all speakers but do you really want your lounge looking like an antique shop?

I have been buying and selling used audio equipment for over 45 years and will assure you that that any pair of speakers that was built by a well known and respected manufacturer that originally sold for $40,000.00 will not sell for $4,000.00 ten years later, unless they are stolen or heavy damaged, the average price of such speakers would be $13,000.00 depending on condition. After consulting several experienced techs who have worked on $40,000.00 (there is not many) all agreed that the quality of the crossovers and drivers in a $40,000.00 speaker that is ten years old would be considerably better than a new speaker that cost $4,000.00 or even $13,000.00 today. 
We don't normally invest in speakers that are over 15 years old (unless there classics) and most of the problems we encounter with speakers of that age is not from parts going bad but rather from misuse and or abuse, a few examples are (1) Exposing a speaker to direct sunlight for ten years will fade the finish and deteriorate the surrounds (2) Over driving your speakers or clipping your amp, can get you a big repair bill or maybe worse, the knowledge that the speakers can't be repaired at all.