So I couldn't for the life of me figure out why Animal Crossing: City Folk played so badly on Dolphin on my computer. Then I happened to uncheck the "Enable USB keyboard" option under Wii in Config. Now it runs at full speed. So in case anyone else runs into a similar problem, there it is!
Animal Crossing works really well on Dolphin with a mouse, I have to say. I still might bust out my old GameCube-controller-to-USB adapter down the line, though, if only because my Logitech G5 clicks so loudly and Animal Crossing is such a quiet game.