Yesteryears' expensive speakers compared to modern moderately expensive speakers

For the purpose of this discussion, let’s assume that ...
Yesteryears’ -- 10 -15 years old
Expensive speakers -- $25,000+
Moderately expensive speakers -- $8,000 -- 12,000

I often wonder if it’s worth paying 50% of the original retail price for older speakers that were considered state-of-the-art and flagship during their day. So let’s say an expensive Sonus Faber was around $30,000 in 2005. The seller is asking for $10,000 in 2018. Is it worth paying the asking price, or is one better off buying, say an Olympica III, brand new for about $13-14k (maybe less with dealer discounts)?

I feel that due to trickle-down effects and manufacturing advances and efficiencies, the modern speakers are as good, if not better, than speakers that were twice or thrice the price ten to fifteen years ago. Is this a valid assertion? Or do you guys feel that speaker technology really has not advanced to that extent? In other words, is a flagship speaker worth $30k a decade ago still going to outperform a new one at half its price?

The reason I’m asking is that I am going to save some $$$ this year to buy a speaker in the range of $8000-12,000 in about 6 - 7 months. Since it’s a pretty substantial amount (for me), I am planning to do as much research and auditioning in the next few months. So might as well get started now. Given that it is really difficult to audition used speakers -- not that it’s easy to audition new ones, but at least you can if you try, should I just strike used ones (ones that were uber expensive a few years ago but more affordable now) off of my list and just focus on new?

P.S. -- I’m just using Sonus Faber to illustrate my point, otherwise, I’m very open to anything that is in that price range. I am purposely not turning this into a discussion on what I like, room size, music preferences, etc just yet since I want to stay focused on the topic -- yesteryears’ expensive speakers vs not-so-expensive modern ones.

P.S -- I understand that Tekton is going to render all other speakers obsolete in due time, and I respect the opinions of those who agree with the assertions, but please understand that it is not going to be on my list. Period. I will really appreciate if we don’t turn this thread into a Tekton battleground.
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A bit off the main point, but I would strongly prefer a smaller speaker with better resolution (like a monitor) than a larger one with more power and better bass.  Also, some speakers are a better value than others as long as you're not primarily concerned about name recognition and resale value.
In my experience I bought a far larger and more expensive speaker system, but I may have been better off keeping what I already had.  It wasn't quite as good but was pretty close (diminishing returns), and I didn't need all that extra power.  I'm still happy about my decision, but I'm reminded of the new Magico M6 speaker, which is better than all that preceded it, and THEY were so much improved over the previous designs, etc.  The same goes for Wilson, Rockport, Kharma, and on and on.  Imagine being disappointed with a $150k speaker since it doesn't have the most up-to-the-minute technology.  Or can you wait at least 10 years and just buy music for awhile instead...?
In the specific case of Sonus Faber, I would take the 2005 $12K speaker (Cremona) over the current $12K speaker (Olympica III). The company has changed and I simply like the old technology better than the new technology.

Two points - companies change and technology updates do not always sound better to everyone.

That said, the older Cremona are hard to drive and probably require a more expensive amp than the newer design Oympica III. Off course, an older high end amp may be the same price as a current mid level amp.

My current setup (Cremona and a Mark Levinson 432) can be purchased used (if you can find them) for less than the price of just the current Olympica III.

Of course, it really depends on what sound you like.

By the way, you can sometimes get a pair of SF Strativari for $20K, which would blow away the Olympica III at $13,500.
What almarg said +1

An improvement in speaker technology should result in better sound. Better sound is quite subjective. 

As for manufacturing efficiencies, those are often achieved by sacrificing quality.

Speaker technology has not advanced enough. A 10K used speaker (over ten years old) and sold for less than half list price would probably cost close to 40K new today for similar quality. Remember that inflation means prices double every ten years. The only reason inflation might be less is if manufacturing moved to China.