I don't think the writing process for movies matter to the GA. All that matters in the end is they get a fantastic sci-fi epic with a great story and memorable characters. The story for Avatar wasn't anything special, and the "mystery" surrounding the movie has worn off(When there shouldn't have been much to begin with since the story wasn't that original). The special effects and CGI will be what mainly draws people in to the sequel, unless Cameron proves me wrong and delivers a better story this time. Star Wars, on the other hand, has always been well received by the GA(long before Avatar) and is huge with children and adults... heck, it's huge with pretty much anyone. Even if you're not a Star Wars person, you know the characters and some concepts of the world, like Jedi and the Force. On recognition alone, I think Episode 7 will pull in more cash than Avatar. News of an Episode 7? That's huge, and it's way bigger of a deal than news of Avatar 2. People are genuinely excited.
And with these new movies there's even more of a chance to bring in people who weren't fans of Star Wars before.