Notably, nopn-jazz/classical musicians who are/were out of the mainstream tend to have greater credibility insofar as being "artists" and, not coincidentally, they are (IMO) more likely to make quality work as they age. I would point to people like Robert Wyatt or Scott Walker in that regard.
Of course, people outside the mainstream aren't lured by brand preservation in the same way that the "legacy" bands from the same era are. Most bands who achieved some degree of fame in the 60s/70s/80s are nostalgia acts, because it's the most lucrative path for them. Most of their recorded output is not any good, but some of them barely ever make anything new anyway, so there's no way of knowing if it would have been.