I think this interview pretty much shows that even back then the idea to use StarWars as a cash cow to realize his ambitious project of a "filmmaking research facility" had already rooted in his mind. The prequels with their heavy accent on special effects and mediocre attention to plot and emotionality reflect him being mostly worried about the special effects and the evolvement of the filmmaking process (which seems to have been his main function and concern in ESB and ROTJ already). Perhaps if he hadn't done the mistake to do everything himself again in the prequels, the PT might have been a lot better.