Older machines will usualy have a better build quality for the same price point compared to today's units. This is something that I appreciate, even if it does not automatically translate into a better sound quality.
My 1983 Sony CDP-200 is not as precise in the high frequencies as most units a few years older that I posess, from 1985 to 1989, but man is it build solid! It is the only CDP of that generation I can say I've heard, so I won't make a generalization.
My second oldest is a Luxman D-103 from 1985. It has a lot of Toshiba inside and performs very well, better so than the older Sony.
My other luxman that I like a lot is a 1989 DZ-112. It is not as well built as the D-103, although acceptable and sounds a bit better to me.
My current favorite is my Sony CDP-505ESD. 1987 IIRC. Nice enough build quality and has the TDA1541 DAC that someone else mentionned earlier. I very much like how this one sounds.
In fact, I don't have that much experience with CDP's after ~1995. I did hear a bunch, but no extensive listening.
Even if technology did evolve and everything, some of those old CDP's are still nothing to sneeze at.
az