For the "future" of the Star Wars series, you can always read the books. S ure they're subject to being retconned at a moment's notice, and sure, the bulk of them are CRAP, but they're there for the reading if you want. PErsonally, I recommend the first six books: the Thrawn Trilogy by Timothy Zahn, and the Jedi Academy trilogy by Kevin J. Anderson. The Zahn books ARE Star Wars. The Anderson books are pretty good, but nothing amazing. Still, they're a damnsight better than anything else. I'd stop reading after that point.
As for Lucas, I think he definitely made it up as he went along. What ticks me off about the guy, though, is that he seems compelled to try to convince everyone that he was right, that he never made a mistake, and that this was all part of his grand plan all along when CLEARLY it wasn't anywhere near as defined. When he says things like "I mean, I ALWAYS intended this to be Anakin's story" you can't help but want to smack him in the face with stuff Gary Kurtz has said in interviews, or that HE HIMSELF has said in interviews in the past which DIRECTLY contradict what he's saying.
If he just came out and said "Yeah, I toyed with the idea at one point, but the direction the story ended up taking, I just don't really see a 7-9 really fitting. The discussions about doing 7-9 were more when we had way more material than what we ended up using, and we thought we needed to do three trilogies just to tell it all. Then we figured it was a much better idea if we cut out a lot of the extraneous stuff, and just do it in a single trilogy. I ended up doing the prequels mostly because I'd just become so fascinated with Anakin as a character when doing all the backstory stuff for the original films that I really just wanted to tell his story."
If he made it clear that it was an evolutionary process, rather than repeatedly saying stuff like "I always intended...." followed by directly contradictory statements, I think the public would think much better of him.
It's the rigid insistence on "No, no, you see, I was right all along. I've ALWAYS been right. I'm NEVER wrong. Everyone ELSE got it wrong by misinterpreting me..." that pisses me off the most.