I don’t remember where I read it, but supposedly Lucas did set aside some of Jedi’s budget to “complete” the Jabba scene in Star Wars. He even initially asked the art department to design Jabba in such a way that he could be more easily composited into the scene. Obviously the idea was abandoned.
I’m willing to meet Lucas halfway on the Jabba thing. I do think he wanted an alien creature in that scene, but the idea was dropped by the time it came to actually shooting it.