We go to a renaissance festival several times a year, and few of the patrons even know that there is a story line to the festival....and they don't care. We rarely even bother with the story line, but spend our time exploring the faire, its entertainment, shopping and food choices, and if we do stumble across a storyline activity going on we might stick around to watch it, but if we haven't seen what leads up to it we might not bother to follow it any further.
Is a story line or backstory interesting? Yes, but possibly more so to serious "theme park insiders" than most guests. It will be interesting to see how successful Disney is at getting more than the above mentioned handful of annual passholders involved.
Lame backstory. It won't make up for the Harry Potter Diagon Alley, which is just amazing.
If any place should have the backstory, they missed out with Main Street. Main Street used to have an authentic experience, but they turned it into a generic mall. They missed the boat with the New Fantasyland. I don't see how they can exploit the immersive land experience without starting from scratch and build it from the ground up.