Lucas said many times that he loved watching Flash Gordon and serials as a kid, and based Star Wars roughly on them. I've heard the whole Lucas wanted to make Flash Gordon but couldn't get the rights thing, but I've also heard that isn't true. I think that people got that idea from hearing Lucas talk about watching Flash Gordon as a kid, and wanting to bring something like that back. But not Flash Gordon specifically. It wouldn't of made sense, especially considering the lenghts he went to to insure that he kept the rights to Star Wars, and not give them up to the studio. As for the Dune one, I have no idea on that one. The Star Trek idea I don't beleive, considering that Paramount had largely forgotten about Star Trek until Star Wars got big, and the Paramount execs were sitting around trying to figure out a sci-fi project they could come out with like Star Wars, and someone remembered Trek.

Lucas might of wanted to make fluff, and then got more deep and psychological after things like ESB. Indiana Jones would somewhat fit in with this, and is certainly a serial-type hero. Many of the scenes in that one were directly taken from serials made in the 30's and 40's.