If the characters are well balanced, no harm will come from having more of them. Sure I'd rather have more balanced characters, but if they do just as good a job, with even more of them, then sweet.
Mewtwo, Pichu, Game & Watch and Iceclimbers are all unique ideas for characters. Pichu being limited with his own damage. Gameand watch being 2-D. Mewtwo.... k well really, I just like how he holds items with him mind. That looks REALLY freaking cool. And I WOULD definitely miss that. lol
Anyway, the only ones I'd REALLY miss losing are the IC. The idea of varying your play style depending on whether you have one or two, and the ability to combo + double team all by yourself. Very cool concept that might be lost If they're removed.
Like you said, I wouldn't necessary miss any of them for their characters, but the I don't know who they could replace the IC with... and even If they did, they'd just be criticized for new character being a "clone" of the old IC.