Honestly I think we can move A Goofy Movie out of the underrated category, When I was in the Disney parks recently there was so many T-shirts, pins and even some candy based around the movie
Max was also a walk around character I saw a few times and heard I 2 I and Stand Out on 2 non-consecutive occasions in 2 different gift shops. the movie is finally getting it's flowers and that is a good thing.
Using this metric Atlantis and Treasure Planet had a few pins but nothing other than that. Still quite underrated movies (although I have some gripes with the second half of Treasure Planet, still a good movie, nothing else quite looks like it.)
We wanna talk about a really underrated movie, Meet The Robinsons, Disney likes to pretend they never made this movie, but it is good and makes me cry like a ***** every time I watch it.