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

Prices.

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  ????

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.

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.

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'm quite on line with Craig and Albert. Digital has improved, but so have cartridge designs. Also speaking of amps and preamps I would contend, that Spectral preamps have evolved more through the years than their amps, with the exception of the arrival of the 360 monos, which are in a class of their own, and the technology of which has now trickeled down. What certainly has NOT improved, musically, are tuners, quite to the contrary actually, I find. Cheers,

I agree with Albert. And would just add that digital has improved HUGELY since its introduction in the early 80s. Cheers. Craig

If we are discussing brand new product, this becomes a design and parts quality issue and not just endurance to have survive the decades.

I would choose the twenty year old amp matched up with the best modern pre. I actually get excited about several of the old amp designs but do not share that emotion with old preamps.

Couple different things going on here. First, both amps and preamps have made important progress, but in different directions. Amps sound better now. Preamps do more/different things now. From purely a sound perspective, I'd vote for amps having made more important progress (especially in the power department versus 20-30 years ago).

Secondly, preamps age poorly compared to amps. The preamps of 20-30 years ago used electro-mechanical switches, buttons, knobs, etc many of which have broken or taken on undesireable electrical characteristics. These have lost their resale value.

Amps are more exclusively electrical devices, often with only one moving part, an on/off switch, which may not be used very frequently. The first things that go are typically the capacitors, which can last more than 20 years in many cases. They are also relatively easy to replace when necessary. Amps last longer than preamps. This is true for tube amps, too, so long as the tubes can be replaced.

Preamps have more moving parts so they tend to get more wear and tear . Designs for the most part are probably of a more simple and straightforward basis in preamps. Less is more kind of thinking. Gone are tone controls , phono options, contour buttons, high and low filters. Remote control has been the biggest addition in the preamp market. Less tuner / preamps are out there also. Amps seem more similar through the years. Binding post improvements are usually better.