some 70's and 80's receivers seem to be popular

Is this just nostalgia? I thought the concensus was that even the best solid state during that era was harsh and hard to listen to for long. That is certainly my memory. I almost quit listening to the stereo back then, until I got tube amplification and realized what the problem had been (well, having been suckered into switching to cd's was also part of it). But now some of that equipment seems to attract fans and bidders. Are they just dreaming?