All three of your responses beg the original question: Do undecided voters look at substantive issues? You seem to think they do. I'm not so sure.
In a wartime situation they certainly do, as noted by the fact that they vote for the incumbent.
Moreover, they will remember what was said not what they saw.
Yes, undecideds want to pick the right man, but they are more afraid of picking the wrong one and will be more conservative in their vote, choosing the leader they know over the one they do not.
Kerry had to convince them that he was the one to lead the nation, and he did not do that.
He won debating points, but lost the campaign.