20 year old solid state technology.....

I have an older Belles 250 amp...class a/b...and have been amazed at how this amp sounds even in regard to the best that is out there today...regardless of its age...which is circa 1987...at any rate...was this statement product by Belles that much better than the competition during its time...or has electronics at this level not evolved that much outside of "subtle refinements"?....
I would tend to agree with the latter.
Open up a 20YO SS amp and one built today and you're not going to see much in the way of differences ihn any of the major parts. In fact, most of the parts will be made by the same companies!
The latter. get the unit modded if you can, but don't use any sleep. The "real" refinements of the last twenty years have been with source components (CD players and analog front ends).

I don't agree with respect to SS evolvement. 20 years ago, semiconductors could not handle as much power as the ones made today; more were needed for a given power output. Today these devices can handle more power so, at least on paper, less devices for the same power rating should yield better performance. I'll be willing to bet that if the Belles 250 had today's semis, it would sound even better IMO.