I was talking with a guy at my FLGS and he was saying that he thought more factions actually make a game more interesting and help to balance a game out better as well. He was using 40K as an example.
I guess the idea is that if you have a faction that currently is underpowered, you can give it something to help it out WITHOUT helping out things that don't need help.
I don't know if I necessarily agree, but I was curious what you guys thought.