I don't think anyone thinks this will compete with HP or SWL, even Disney can't believe that. They are both global, with multiple stories, with hardcore fans who have these IPs part of their lives ad celebrations. Avatar is a one time big hit movie that no one I know talks about or even remembers (except how long it is). I mean no one says "hey, let's have an Avatar festival"... What it brings to Disney is it's beauty that is "out of this world" and could truly be back drop for lots of stories. There is always a market for merchandise based on fantasy and that is who is buying, they are buying for the fantasy, colors, uniqueness of products.
My DS knows nothing, understands nothing of Avatar. Loved the land and loved FoP calling it Flying Dragon. He wanted to buy a Flying Dragon. As long as the money flows and that park if full, Disney will consider it a success.