In the last 20-30 years, what has changed most...

I agree with Albert and his idea of preferring and older amps over and older preamps. Let's see, 30 years. That would make in 1972, huh? The dawn of the quadraphonic era - about the time when the notion of my old Marantz 4400 receiver was hatched in someone's brain.

I have listened to some very, very good systems in the past year or so and I can't honestly say that any sounded materially BETTER than the best of the systems I heard 30 years ago (although my ears are 30 years older now, too!).

What HAS changed is that folks are spending more on ONE interconnect than was spent on entire SYSTEMS thirty years ago. Inflation or not, this is scary.

I would not even mind going back even further on amp designs. There were many built at the dawn of the era of HI Fi that are still valid today.

First that come to mind are the Western Electric designs, the Marantz 16, Macintosh 225 and 275 and HK Citation.

Even the old Dynaco Mono's are still a very valid amp, even by today's standards. All of these benefit from the great tubes supplied in them from the factory, the same tubes we are scrounging around to find as NOS or clean used, even today.

Oh me God, Albert, the Western Electrics! Awesome (pls excuse the expression)! Listened to a modified such sys in Paris, running off a Detlof type Goldmund ref TT and, yes, it was more than impressive. The speakers were horn-loaded cinema gear, also WE, salvaged from some sale in the '70s.
Nothing that fits in the modern Euro-home. I wonder if it fits the average US home, even. But, by memory comparison, my sound (in a 23/13 room) is sadly compressed.

Well are Flat Screen TVs included because what has happen there is Unbelievable .The quality of the picture and the size you can have in your home and the price .While audio equipment has gone thru the Roof...Flat Screens have Dropped to Crazy Prices.85 "to 100". $2,000 .For picture quality ,the freaking people on screen are in the room with you.How is this possible  ????

Prices.