I HATE, and I do mean HATE, Avatar, and even I know that this will make a cool attraction. Avatar, in my humble opinion, has a horrible screenplay and laughably cliched characters, but it also has gorgeous art direction and design. If there ever was a place where the sheer spectacle is more important than writing (dialogue, plot, etc) it's a theme park attraction.
And $500 mil to start with is a lot. That's two FJ's (if I am remembering correctly).