I disagree, having been to Cars Land. If you haven't seen Cars, you're basically in this nice-looking cavern with some cool rides. If you've seen the movie, you realize you're in the middle of Radiator Springs and you understand the attention-to-detail in the land so much more, like why every third blink on the traffic light is slower or where the music comes from during Radiator Springs Racers. You just get so much more out of it where it goes from being, "Well, this is nicely done" to "Holy carp, I'm in the middle of a movie." It takes it to the next level. (and yes, I told my friend that Cars is required viewing for the trip to Disneyland in January and that if she does not watch it, we will watch it in the room the first night we are there).
It's one thing for the dark rides to never have seen the movie. You get the general idea just by riding the ride (and PofTC the ride came before the films, so nothing really to gain from watching the films for that ride). But for these lands where you're in the middle of a movie, you get so much more out of it if you've seen the film. I had no interest in seeing Avatar, but I watched it so I understand the elements in Avatar Land, and I'll watch it once more before going.
Besides, every person should watch the original trilogy films at least once in their lifetime. Star Wars is just one of those films that everyone should see once. Not that I expect my father to ever become a Star Wars fan any more than I am a James Bond fan, but I've at least watched the James Bond films before forming that opinion. Same with Godfather and Gone with the Wind; I don't like either of those movies, but I watched them because they're classics that should be watched. I watched Star Wars initially because it was a classic to be watched, and it turns out I love Star Wars.
My mom has seen the original trilogy now that I'm a fan, and while they're definitely not her favorites, she's learned to appreciate them. My dad has refused to watch them, but loves Darth Vader.