I think that the additional material was a main part of the appeal. To be fair I mostly remember that from the initial episodes - perhaps you're right that it becomes more padded later. Still, it's pretty well-done overall, I thought.
I have another audio Star Wars that I enjoy much more:
Lux Radio Theater's "The Adventures of Luke Skywalker". This was basically a fan production, done in the style of a 1940's radio drama, with the voice actors mimicking specific famous actors from that period. The "cast" included:
Luke: Mickey Rooney
Han: Humphrey Bogart
Leia: Katherin Hepburn
Ben Kenobi: Jimmy Stewart
C-3PO: Oliver Hardy
R2-D2: Stan Laurel
Chewbacca: Rin-Tin-Tin
Darth Vader: Bela Lugosi
Tarkin: Erich von Stroheim
Uncle Owen: Jack Benny
Aunt Beru: Mae West
General Dodonna: Jack Webb
Red Leader: John Wayne
Red Two (Wedge): Henry Aldridge
Red Three (Biggs): Ronald Coleman
Red Six (Porkins): Orson Welles
Red Nine: Groucho Marx
Red Seven: Harpo Marx
Red Ten: Chico Marx
Gold Leader: Curly Howard
Gold Two: Larry Fine
Gold Five: Moe Howard
Admiral Motti: Edward G Robinson
Commander Tagge: Peter Lorre
Imperial Commander: Basil Rathbone
Imperial Officer: Claude Rains
Imperial Announcer: Boris Karloff
Greedo: Keye Luke
These were all portrayed by six different actors in multiple roles - plus a seventh who was purely a narrator. The performance ran 90 minutes, covering just the first movie. I saw it as a live performance at a convention in San Jose - subsequently I bought a CD recording of it (actually from an earlier performance):


While the cast didn't
look anything like the famous actors they were mimicking, they did at least dress up as voice actors might have in that time period. You also got to see the sound effects creating all the sound effects live, which was pretty impressive in itself. I think the only thing they didn't recreate live was the music, which was freely taken from John Williams' soundtrack played on an ancient gramophone. The whole thing was remarkably well-done, and recognizing the voices as they appeared quite a lot of fun. I think Jimmy Stewart as Obi-Wan worked particularly well. And you can never look at Aunt Beru the same way again after you've heard "Luke, come to dinner!" done with the voice of Mae West.
