I have mixed feelings I guess. I've not played Animal Crossing so can't comment on its suitability in this particular example. In general though, I don't think that they should be shoehorning Miis into everything as this could compromise the characterisation in the games. Having said that, there is something very appealing about personalisation and this works well in less involved games like Wii Sports. My other half (non games player until now!) loves the fact that your player on screen is a representation of yourself.
I love the idea of getting clothes etc. in games that you can use to dress your Mii. Also, I want to create a Mii of my cat so if I could get a pet that would be cool .