However, I have found in the past few years that the genre has hit a "plateau."
It's as if most of the rich veins have been mined out, and you only turn over a nugget now and again.
Again, that may well be simply my subjective experience. But I still belong to the SF Book Club after all these years--about twenty-five--and every time I read over the new list of stuff coming out, NONE of it seems appealing to me in the slightest. In fact, they've sort of turned to the "punkish" strain, which is full of characters I can't relate to, and don't like, to churn out more stuff.
IMO, there is no new Larry Niven, no Clifford Simak, no Scott Card, no Vernor Vinge coming over the horizon. It's all people who grew up reading comic-books (and NO real literature) and just emulating what they know.
Again, maybe it's just middle age--I'm 44--but that's the way it seems to me.
The best thing I've read of late in that genre are the Discworld novels of Terry Pratchett (which is really a send-up of the whole genre, anyway; a parody) and the "Song of Fire and Ice" series by George R. R. Martin (another old-timer; and this is Fantasy anyway).
Gene Wolfe is another who keeps churning out high-concept material, but again, he's an old guy.
I would be more sanguine about defending SF as literature if it didn't seem like it was in such need of vibrant new voices, of the same caliber and vision as the group of young turks who Harlan Ellison featured in his "Dangerous Visions" series in the late 60s-early 70s.
Scott Card is, in my own experience, the last "new" writer of any real worth.