The Jabba scene. First of all, I have to say (inspite of the poor CGI effects) that I like the scene. I always have. Ever since I read it in the novelization of Star Wars. Now, if I remember correctly, in the novel Jabba isn't described as a huge slug. I would have to pull the book off the shelf to verify this, but I seem to recall that Jabba came across (at least to me) as just some crime lord who Han happened to owe money to. For me, I have always felt that the scene needed to be in there just because I think seeing Jabba is important. I understand that not seeing Jabba until Jedi does add mystery to the character and makes his reveal in Jedi that much better. Yes the scene was cut because it was redundant. Some one even states this in Empire of Dreams. I just happen to like the scene and I'm glad that it is in the film. Granted, they still haven't gotten Jabba to look right in the scene but the way it is now I can live with it. It's far from perfect. And yes, it has been known for years (and even stated by Lucas himself) that as ROTJ progressed the design for Jabba changed. I serioulsy don't think that Lucas really had anything in mind at the time the original Jabba scene in ANH was filmed.
Now, if anyone has listened to the commentary on the new DVDs Lucas himself states that he never intended to go back and film the prequals. I don't remember which film he states this on, but he does say it. It was only after the ground breaking CGI of Jurassic Park that he began to think about the prequals. Lucas states that they way he originally invisioned the trilogy was that of a Saturday Matinee serial. I don't remember his exact quote on the subject, but that is why he started with Episode IV. He simply wanted to drop the audience right into the middle of the story and he really never had any intention of ever doing Episodes I-III. Yes, I know that he wrote an outline for the back story, but that was more for his own use to help him shape the story of Episodes IV-VI. This at least makes sense to me.
Now, all of the above is completely contradictory to what he stated in 77 and 78 that the whole story was a 9 part saga. I do believe that it was a nine part story, but I don't think that he really intended to go back and film the rest. If you look at IV-VI, it's really not necessary to see the events of I-III. All of the pertinent events of I-III are mentioned in IV-VI. As a kid and later as an adult, I did speculate on what had led up to Anakin becoming Vader, but in all honesty it wasn't all that compelling for me to see it. As I stated all of the important information is contained in the original trilogy.