Amp improvement since 1994?

It depends on what you mean by "real" improvement. Probably nothing that can be measured.
I do agree that the trend seems to be towards transparency/resolution and away from musicality, but I'm not sure that is a good thing. My old tube amp beats most of the modern amps out there now, IMHO.

As to your last question, where the gains have been, I would suggest mostly in the price tag.

Interesting Timrhu. Audiolabrinth, I realized dramatic transparency improvements from power supply improvements. Experimenting with balanced isolation transformers, various conditioning devices and MIT networked power cables has improved my preamp (reputed to have a 'very' high quality separate power supply)incredibly. I believe the power supply was definitely the weakest link in my system.

Look at power supplies in the newest Rowland amps - they are line and load regulated high frequency (1MHz) switchers that are extremely quiet. For that reason he uses switchers in preamps (where efficiency plays no role) - instead of linear power supplies, that in reality are noisy unregulated primitive switchers (but easy to design).

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Plenty of improvements
Take Pass Labs for example. The new supersymmetry is amazing!
Real designers are constantly pushing the edge of what is possible.
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Yes, plenty.

Smaller, lighter, more efficient, more power, lower noise levels, more compliante, you name it, improvements pretty much in every way. Technology moves ahead significantly in all ways in 20 years.