The Gnomes are more dangerous than they look, simply because they're the only Illuminati that can win playing defense. If they get a few high-income groups, and then get to sit back for a few turns and build up cash, they become almost unassailable. It's important for other players to cooperate to hit them regularly and bleed off some of their cash. It's also a really good idea to try to keep track of how much money they have.