I think a sci-fi musical could be done well. And if we're talking about films that could be improved on in a remake, Just Imagine! then, could be one such film.
In terms of the sf musical, there was REPO! The Genetic Opera a few years ago, but despite it being eternally available for free on demand, I've yet to see it. There's also The Phantom Empire, a serial from 1935 starring Gene Autry. Supposedly it combines the musical, the western, and sf, although I confess I haven't seen it, either. Beyond that, it's a pretty empty genre. Would Dr. Horrible count?