Yeah. New characters are nice and such, but they aren't really a must in my opinion. (Add-on characters tend to be really gimmicky too.)
I would rather have them fleshing out the old characters instead. Hoenn has very many characters who have potential to become even more interesting, like The Trick Master, Prof. Cosmo, The Winstrates, Captain Stern, Gabby&Ty and some others. All of them have relatively small roles and I certainly wouldn't mind if they got larger roles.
I agree with this. The characters you have listed have more potential to be developed further imo. It would be nice if Mr. Briney and the Frontier Brains would make more appearances