are 4000$ /pr speakers today better than $4000/pr speakers from mid to late 1990's?

 Inflation!
The U.S. dollar experienced an average inflation rate of 2.09% per year during this period, causing the real value of a dollar to decrease. In other words, $4,000 in 2000 is equivalent in purchasing power to about $6,045.99 in 2020, a difference of $2,045.99 over 20 years. The 2000 inflation rate was 3.36%.

Specifically to B&W I’d unequivocally say buy the newer speakers.  I find their newest tweeter and midrange drivers to be far superior to those of 90s vintage. 

Here is something interesting. In the last ten years i have owned Devore, Audio Note, Harbeth, B&W, KEF, Tekton DI`s and Magico speakers with prices ranging from 4k to 19k and while all were good to very good i was never 100% happy. Recently i came across a nice pair of Wilson Watt Puppy 5.1`s for 4k and i will tell you in my home and paired to my system the 20 year old 4k(todays used price) Wilsons out perform all of the above mentioned speakers.

I know 20 years ago the Wilsons were something like 17k but at todays used prices they are out performing some of todays new 17k speakers.

@soix ,
Have you read the latest Stereophile review of the B&W 705?
There are some interesting comments regarding old and new  BandW's.
B

speaker design has advanced a lot, materials got better but i feel that in many modern cases tuning is missing.
G