I'm not claiming the politicians would be more honest, I'm claiming we would see less idiotic arguments, which to my eyes counts as "more reasonable political debate".

If two people debating publicly are dishonest, willing to lie or mislead when they can get away with it, and are not trying to refute their own argument the way a truth-seeking rationalist would, then increasing their intelligence only improves their techniques, it doesn't force them to be more honest.

Again, the biggest effects doesn't come from improving their intelligence, but improving the public's intelligence: even if those two people stay completely dishonest, a smart public shifts the topics they can talk about; instead of birth certificates and conspiracy theories and Jesus they can talk about fiscal policy and other substantive issues (even if they lie just as much as before!).