"The less a game character talks, the more words are put into his or her mouth."
Kind of quoted (paraphrased) from the RPG cliche list (not sure if it's still online). I think that's sort of true. Just look at how the animals react to you in Animal Crossing. They assume that you think all kinds of things about them, but it's just because we can't talk to them and tell them "I like you, Bob." or "I hate you, Valise." *animals picked at random*
I think there should be slightly more voice acting than there is now. Just enough so that Mario doesn't have to act out everything he's trying to say, Luigi can object to going on the adventure, Link can tell Zelda not to do that thing she's about to do, and Toad can tell Mario that the Princess is in another castle.