Affordable vs. ultra expensive speakers - what's the difference?

Nothing. Absolutely nothing. That’s the answer you’re phishing for, right?

I think there is a difference but not sure if 50K difference.

I understand the diminishing return of higher cost speakers.  In term of driver technology, both speakers seem to be in equal.  The monitor metal dome technology does not seem to be inferior vs. the yg speakers.  They are not of garden variety but the product of extensive computer simulation.  In term of cabinet, the YG cabinet is made of aluminum so it has some advantage.  In term of xover component, the YG probably has better, higher  price components.

Overall, I think the only thing that justifies the price of the YG is the aluminum cabinetry.  But that alone does not seem to justify the 50K asking price though.

Another part of the equation is there seems to be a rather high jump in price of high end audio components.  Everything seems to cost quite a bit more nowaday.

The Thiel CS2.4 was only about 4.5K USD when it came out.  It can compete handily with the YG.  

Their top of the line CS3.7 was only 13K USD.  How prices have gotten out of whack! 

The 2.4 cabinet performs poorly against some of its more modern competitors

Is a there a link to point to a test that compares the cabinet resonance?  I am not aware of any specific test.

It’s difficult to judge a pair of speakers based on the frequency response plot.  There are just too many parameters.