I think Harry Potter (which I love), has sadly misguided the fan community into believing IP is king in the theme park industry. It never used to be this way and Disney built beautiful and engrossing theme parks without it.
Whether or not you feel Avatar is beloved does not really matter. If they use it as a vessel to build a beautiful world with engrossing attractions, it doesn't matter if anyone knows a character. Many great attractions have been "characterless". Fortunately they seem to "get this" with Avatar. It's Pandora land, not Na'vi Land (or blue sex kitten land as people colloquially love to demean it by). Whether or not you love or loathe the story doesn't matter as long as they take this approach (which the artwork indicates they are).
You know what are mediocre IP's? Tower of Terror, Song of the South, Transformers, Cars.... sure I could go on. Yet they were vessels for creativity that surpassed the IP it was based on, or at least something no longer deemed relevant.
Sure the consensus is that no one will be "rushing" to visit a land based on Avatar. No one would be rushing to visit AK Dragon and Unicorn land either (except the Disney fans who know it as the Beastly Kingdom). They are both crap non-existent IP's that may form the basis for a good land, or it could be total crap, but the IP does not matter.
What matters is people see it, and love it for what it is, not what is is based upon. If it turns into something great (like Carsland), 99% of the people complaining will get over the IP and appreciate what it is. The other 1% will just forgo it (proving a point to no one but themselves) and complain about it on a forum for the next decade, because really they have nothing better to do with their lives.