Coruscant first appeared in the Expanded Universe and was called such for the first time in Timothy Zahn's Heir to the Empire in 1991. Coruscant wasn't seen on screen until the 1997 Special Edition release of Return of the Jedi, and then later appeared in the prequel trilogy. Coruscant is therefore one of the few EU elements that made its way in to the films.
Also: The Prequels didn't retcon much of worth from the stuff that came out prior to TPM anyway. And what retcons exist, are mostly fairly minor affairs. http://starwars.wikia.com/wiki/Retcon
So i'd say there is still a LARGE amount of story that can be drawn from. And I doubt they can come up with anything on their own that is anywhere near as good as the Thrawn Trilogy. Or any of the other 50+ some odd novels out there that expand the story beyond ROTJ.
The point I was making is that the original trilogy is good not because of the universe it's in, but because of the characters and the personal nature of the story.
The prequels showed what the Star Wars story, by itself and without an actual soul, looks like. All the bureaucracy, all the politics, none of that stuff matters to anyone.