And Belle.

All 3 do, but Ariel is fully obsessed with intellectual curiosity about humans. Her determination to collect so many human artifacts shows an intellectual interest in how their world functions as well as a clear passion and you can't be low on the intelligence scale without it.
Belle too, with books. This is why I think Belle's interest in reading DOES indicate high intelligence. Belle's read every book in that library- and I'm willing to bet they're not all fluff books. Her desire for more adventure shows an intellectual curiosity, regardless of if she's bored or not. And, her high intelligence has impact on how bored and restless she is.
Rapunzel, too, obviously.

She doesn't fully understand what the human world is like or what humans are like and is curious about both of them. She's told that they're evil but her curiosity dares to think outside the box and try to learn more about it. She doesn't understand it but she wants to understand something that's greater than she can comprehend. She wants to discover more about a world that she's not part of and never wants to stop learning. She even wants to become human so she can continue to learn more about the culture and have adventures while learning.

agreed with both of you.