Actually, we do have proof positive that the more juvenile tone would have sank the first Star Wars. It's Lucas's second attempt at a multi-part epic story: Willow. Willow was meant to be a prelude to another trilogy a la Hoobbit/Lord of the Rings. However, Willow failed to perform well enough at the box office to warrant the sequels, which were eventually made into novels. I've spent a good deal of time wondering why I don't like Willow. The reason is that the lame attempts at humor just didn't work for me. Sure there were some good attempts at humor, but there was also bad one. I think the movie lost me when Val Kilmer was rolling down a snow covered hill and got rolled up into a giant snowball. Why a stupid cartoon gag was used in an action/adventure/fantasy, I have no idea. But Willow is what Star Wars would have been if George had his way with it. And in spite of the 'see cows' story above, I think that is what he was after. There have ben enough behind the scenes rumors to make me believe that the tone of Willow or the prequels/SE was what Lucas wanted.