I don't agree. I don't think the movie plot itself will ultimately matter. People wanted to visit the land, shouldn't really have anything to do with the plot of the movie. People should just put it out of their minds and appreciate the land for what it is. Why are you trying to undersell it for yourself?
Most will probably enjoy it for the land it is. It's not going to go away, it's here ...
You're right. The plot doesn't matter. Lots of movies with awful plots could make good modern IP lands (Star Wars prequels, DC Universe films, etc.) and plenty of films with wonderful plots couldn't (a vast majority of the great films made prior to the advent of the blockbuster in '75, for instance).
To provide strong inspiration for a traditional land, the bare minimum an IP should do is present a unique (Avatar does) and varied (Avatar doesn't) setting that a large number of people are predisposed to want to visit (I'd argue Avatar lacks this as well, but your mileage may very).
Modern IP-based lands are not designed and built purely on their own merits, however. They are meant to be an integral component of the serialized franchises that came to dominate Hollywood in the early and mid-2000s. To do this they should be situated clearly into this narrative and, ideally, offer new, relevant story information. This was not possible for Pandora since it was based on a property with only one film that, unusually for a modern franchise film, resolved its story and left no obvious cliffhangers or hooks for further narratives. This uncertainty about the eventual shape of the narrative is a significant reason why Pandora is set hundreds of years after the close of the theoretical final film. Disney and Lightstorm are trying to ensure that the land interacts with other elements of the narrative as little as possible - exactly what an IP-land shouldn't do. Even if an incredibly interesting character appears in Avatar 2, for instance, they'll be long dead when we reach Pandora.
Such lands should also ideally feature a wide variety of goods and foods featured in other installments of the franchise. Avatar's themes specifically rule out the range of consumer goods that are vital to IP lands, adding to guest immersion and corporate profits.
Finally, such lands are intended to draw and grow existing fan loyalty via the integration of details - structures, characters, signs, etc. - that have meaning within that particular fan base. In fact, these details are often given their significance and backstory, in whole or in part, by fans. Lightstorm knew this, and intended to use fans to flesh out the underdeveloped history and details of their world, but to the best of my knowledge little came of this. The upshot of this is that Avatar remains a very broadly drawn property, with details well-defined neither by fans or Cameron and his collaborators.
The fact that Avatar is a poor IP for a modern theme-park land has little to do with either its plot or its overall quality.
On another note, you have a tendency to boil my (very long-winded and largely unnecessary) observations about Pandora down to "I don't like," which is a bit passive aggressive. I might as well say that certain folks here are determined to love the land regardless of its quality.