I have to admit that I am not really keen on modern and post modern music. What you call the science fiction opera seems to be a genre of postmodern music that synthesizes a lot of modern strains of musical "developments." I took a really interesting post graduate course that was called "fragmentation and integration" in arts. The objective was to look at the modern trend of fragmenting "-isms" like minimalism, structuralism, serialism, deconstructionism, etc. and see if there are integrations taking place. It's a search of a cultural semiosis, closing of the loop if you will, that will establish a meaning in someway. Philip Glass is one man who is on this as a living. There is another person who put out his version of a semiotic masterpiece that integrated a life long journey into music.
That is Frank Zappa!
I think his final work,
Civilization, Phase III is an Opera (now that I think of it) and it is a powerful one.
The epithet of the opera and Zappa's music is in the final dialogue:
Spider: We can get our strength up by making some music
John: That's right
Monica: Yeah . . . yeah
John: But the thing is, you know what?
Spider: What?
John: We don't even understand our own music
Spider: It doesn't, does it matter whether we understand it? At least it'll give us . . . strength
John: I know but maybe we could get into it more if we understood it
Spider: We'd get more strength from it if we understood it?
John: Yeah
Spider: No, I don't think so, because -- see I think, I think our strength comes from our uncertainty. If we understood it we'd be bored with it and then we couldn't gather any strength from it
John: Like if we knew about our music one of us might talk and then that would be the end of that
Doesn't it remind you of the ending in a Samuel Becket Play?

Thanks for bringing up the other ones. I will have to listen to John Adams.