How does one weigh the virtues an older amp vs. a younger one?

My experience has been that for a given level of amp, 10 years and new is substantially better than the older. Not just noticeable, but wow, that is really better. I have been at this 50 years and owned multiple generations of Pass amps from the Threshold s500 back in 1980.

A couple years ago moved over to Audio Research tubed amps. I will not be going back.

Think of an old car with few miles vs a lot of miles. No comparison. Amps are similar, if you can get an old amp that wasn’t used a lot vs was played hard, it makes a difference. I like my Carver 505 that was built in the nineties a lot and I would put it up against any of todays amps up to $1500.

OP, since you are talking integrated amps, how about a Mark Levinson No. 383.  George Meyer in Los Angeles, who is an authorized Mark Levinson repair facility has completely refurbished units at $3,000 dollars and another for $3,200 dollars.  These are outstanding integrated amps.  Here is the info: