It's a short term, money making grab, yes, but have you seen the way Disney forces their movies that are 40+ years old down the throat with "The Disney Vault" because that is going to be what happens with this. I agree with you, themeing a land to a mediocre movie at best is not good, but kids love it. I never understood the Pixar hype, I think most of the movies are severely overrated, but if any (besides Toy Story) were to be built in an area, I am least surprised that it is Cars. If in say 20 years, or whenever it starts to get bland, it won't take more than a few changes to change it to a Route 66 themed area and keep in touch with the California aspect of it.
Disney will also stop selling this movie in the next 3-5 years, making it "exclusive" again, which will attract families. Then (when the next home video format comes out) they will start "unlocking the vault" and release a movie over a short time frame, and sell the **** out of it, regardless of how bad the movie is. Look at Pocahontas, not a good movie by any stretch, but it still sells great because of that stupid vault thing, it is truly brilliant marketing and they know how to sell a turd.