Regarding the question of old amps versus new, there is the related issue of which era featured the very best amps and preamps, and the answer, I believe, is the mid-90's, due to a number of market realities.
First, as other posters have explained, the mid-90's products featured much better parts quality than the gear made forty years ago. Mid-90's gear, however, is also generally better than current products in my opinion, as the two-channel market ten years ago was much stronger than today and supported expensive, all-out product lines (for example, the CAT Limited Edition L-1 monsters and VAC Renaissance line). Today, the market is 90% home theater and as to what's left, manufacturers compete against a strong used market on the Internet and cheap Chinese products.
As for tube amps, VAC and CAT, for example, have abandonned expensive point-to-point wiring in favor of circuit boards in their most recent product lines. Ten years ago, Cary made nothing but tube amps, whereas it now has a full line of multi-channel amps and heavily pushes solid-state amps (which are much easier to sell in a multi-channel environment). The big vinyl mail order houses like Acoustic Sounds and Music Direct now push Chinese tube amps which are mostly $1k to $3k products that squeeze U.S. tube amp makers who have traditionally sold through brick and mortar shops and who have not outsourced production to cheap-labor venues.
The change is also seen in solid-state, a good example of which is Rowland. Ten years ago, the company's cheapest amp was the Model 2, which cost $5,800 (and $8k if purchased with battery power supply) and was built like a battleship. Now, he makes one expensive amp, the 302 (or 301 in monoblock form), and everything else is comparatively cheaper ICe powered amps that are specifically targeted at home theater. Ten years ago, Rowland made the $14k Coherence II preamp with battery power supply and its cheapest preamp was the Synergy II. Now, the Synergy II is Rowland's top preamp, which retails for about 1/3rd the price of the Coherence (to Rowland's credit, they clearly state that the Synergy is not the equal the Coherence), and there is a much cheaper Concerto preamp.
I am not at all saying that today's new products do not offer good value, but rather, that the golden age of two-channel was ten years ago (which is, I think, the answer to the final question in the line of questions beginning with "is there much difference between the old amps such as Scott and Fisher compared to newer ones like Cary, VAC,or Audio Research").
