It is hard to answer this in general. Here are a few personal impressions. I still have acces to a fairly large amount of Marantz, CJ and ARC equipment that I owned from the late 60's onward (sold to friends, moved to second system). Yes, there are capacitor problems after awhile and you may want to replace them if you are handy with a soldering iron. However some very good ARC and CJ stuff from the 70's that I know is still quite good can be had for cheap (check ebay). I think the advances in very high end power amps have been less than in other electronics. I would never buy an old CD player. Preamps from the early 80's are still decent but unless you want a phono stage built in, the CJ and ARC preamps do show their age compared to newer designs. I think a significant amount of progress was made in speaker performance during the 80's and would be leary of older multi driver systems unless you are pretty sure of the performance. Just my opinion.
