I disagree with you here. Red's face is different and so is his hair. Leaf herself was based off of a character wearing a black suit in the original, but in the remake FRLG she wore a red skirt and a blue tank top. The HGSS heroine is wearing Red just like the girl from Crystal. I think that it is a good idea to wait for an explanation to just to conclusion whether or not a character is designed or was after that character. She could very well have nothing to do with the Crystal herione, but we will not no far so unless Gamefreak informs us somewhat. I know you all going to bash and flame my theories, but that is the way I feel.
I think the girl in Crystal was meant to have more of a tomboyish look - since by their reasoning, most girls playing at that time (or would play if there was a girl character), so they made it similar to the audience they were trying to appeal to. May in RSE kept this sort of pattern.
But Dawn - and Leaf as well -, in my opinion... she just has so much more of a... feminine... look, if you understand, since from my understanding, many girls play Pokémon as well nowadays (at least younger ones), and they are trying to appeal to another audience now (the more 'girly girl' girls).
In plain terms, this is simply a marketing decision based on the audience they already have, and the new audiences they are trying to appeal to.