If you're (and they're) waiting for Toy Story Land over Avatar Land, that is truly a mistake.
But like you, plenty of people may not initially plan a trip for the land. It's Avatar. Creepy blue sex kittens who curse and are not appropriate for their little princesses. But once the land makes a name for itself and people go home telling their friends and family how awesome it was, do you think those friends and family will be booking a trip? I betcha they will be.
The PR junk can only take Disney so far, word of mouth is the ultimate way to draw crowds. Build it, and they will come. The Splash Mountain example is tired but it's true. In the long run, the IP will not matter as much as the quality of what is built. That's true for Potter too. If Potterland was crap, it would not have drawn such crowds. Quality is what matters and I'm optimistic that Avatar land will be exactly that.
Word of mouth is also significantly cheaper than other forms of advertising.
Still, I feel they should've went for something non-IP-based, and that that would've been even more successful. Because clearly the IP will hold some people back, like you.