I think my opinion on Donald and Goofy has changed a little. We've now been with these costumes for so long that they feel like one of the last recognizable vestiges to the start of our journey with Kingdom Hearts. Like, sure, you could try to give them new costumes, but they really already do their job so perfectly it's hard to imagine topping them.
In Toy Box, Sora transforms into a toyetic version of his normal self, with a smooth, plasticky version of his normal outfit. Meanwhile, Donald and Goofy, for some strange reason, end up wearing completely new clothes, albeit in a lower fidelity toy style. Donald is wearing a blue boater hat with a black jacket, and Goofy is wearing a bomber jacket and a green cap with sunglasses on it. Generally, as costumes, these ideas seem too bold and uncharacteristic for Donald and Goofy, and I strongly believe that these are rejected designs for their full KH3 costumes.
It's one of those things they got so right in the beginning that I really don't want them to mess with it now.
For characters who should get an update, I think Namine is due for an update. She's snackin in her short dress but I can't imagine that's very comfortable. Mickey can always get a new costume, although at this point he has so many that he really could cycle through them. Aqua could get an update I guess, but I don't think she'll ever be so important that she'll need one.
Sora can hang onto his current clothes until KH4. Same with Riku and Kairi. We really didn't get enough time with Riku and Kairi, but I find their new clothes to be very cool, especially Riku's.