Not everything they wrote has gone obsolescent; "Nightfall" and "The City and the Stars" haven't, and I don't think they will. Of course, the dialog in "Nightfall" is pretty bad ("you double-crossing rat!"), but those two in particular will, I think, continue to pack enough sensawunda to be readable for some time to come.

Other than those, and maybe a few others? Yeah, you're probably right.