What happens if I find all the lost Dalmatians?

So Pongo and Perdita are missing their puppies, and I sometimes find some of them in various chests I come across.

Is there any point to this side-mission? What do I get for returning the puppies?

For roughly every 12 dalmatians you find, you get a prize from Pongo and Perdita. These prizes range from ship gummies, to accessories and synthesis materials.

Additionally, finding all 99 Dalmatians awards you with an upgrade to the Aero spell, and access to the "Secret Ending" at the end of the game.

Aside from the above-mentioned Aero upgrade and the hidden ending unlock, you also get a complete collection of gummi ship pieces.