Mutants are terrible, while the others basically get a bonus to their primary attributes.
Mutants need to be more badass, though the current system doesn't allow for much. I was thinking special statuses to show you what their mutations were (so when you checked their status you'd see "three arms" and "pincers instead of mouth" and "large insect eyes", each with a different stat bonuses.
For example, the insect eyes could give a small accuracy bonus and an increase in the chance that the liberal's eyes would be damaged when hit in the head. Two heads would give the liberal an intelligence boost and a small chance that the liberal would attempt to perform two actions at once because the heads couldn't decide, performing each at 30% effectiveness or something, and it would also increase the chance of the liberal getting hit in the head. With the cool mutations could come special unarmed attacks (Mutant strangles Conservative with his tentacle arm).They would all drastically decrease charisma, so mutants would be awful ninjas/recruiters.
Basically, I see lots of untapped potential with mutants. They're supposed to be satirical and funny like the rest of the game, but they're just like real mutants: depressingly frail and useless.