It's tough to say on Lucas. There are quotes of him sounding completely sane, and knowing exactly what's needed to make a solid film that both told a real (simple) story and fascinated peoples' ideas surrounding space and mysticism. He knew that the special effects were key, but as Handy(?) stated before me, they were the tools to the ends, not the ends in and of themselves. Then there are other times, when he started in with the Special Edition releases where he said that he'd have done so much more with the special effects had the technology and budget been available to him back in 1976. Well, he got that budget, and you can see what he did to his otherwise great films (IV and V).
Also, he acknowledged that he didn't have the greatest ability at script writing when writing the story outline for Empire, so he brought in some help. Kasdan and Kirshner took a good story outline and made a fantastic movie from it. Then Lucas inserted himself deeper into Return of the Jedi, and out popped the Teddy Bear Jamboree and the unwillingness to kill Han even though it should've happened.