Heinlein probably helped influence me politically without me realizing it. Here were characters who had the same values my parents were trying to teach me, but doing really cool things! Niven... I think it's more his cowriter, Jerry Pournelle, who's the conservative. I know that the Pournelle single novels I've read have been conservative leaning, while Niven's have been more libertarian or liberal.
Other similar authors: James Hogan, who writes mostly hard sci-fi, has developed libertarian/conservative leanings. Asimov seemed to me to be a borderline case: his books had some very liberal leanings, and at other times were quite conservative... I just read John Ringo's alien invasion books a couple weeks ago and he seems pretty conservative - at least there was none of this qimpy "let's negotiate with the man-eating things" nonsense.
So I guess there's some hope yet in sci-fi. I haven't stopped reading it yet, anyway.
I enjoyed reading Heinlein's stuff years ago, when I was an undergraduate. I too was pretty oblivious to political philosophy when I read them, but my parents had also done their best to instill the right values, which came to the surface eventually.
I've tried to teach my kids, who are grown, the same values, that seems to have worked.