Well, I personally have seen Monsters Inc at least three times in the last 5 years. I can ask around tomorrow if you want for my friends. For merch, again, someone got on the bus today wearing a Sulley t-shirt. The general consensus I gathered was that among us high schoolers, it's just a movie that exists in the back of your mind. It's not necessarily everyone's favorite movie, but everyone loves it and everyone can name characters and quotes and stuff. The "put that thing back where it came from" scene was mentioned by two separate friends.
And yes, you have a point it'll be popular because the park needs attractions, and in the beginning because it's new, but also, it is a popular IP that a lot of people love, with a ride based on a scene that people have said should be a roller coaster since the movie came out. So it'll also be popular because of that aspect, and I expect it will be an immensely popular attraction for quite a long time