I Want Your Sex: Much like with the singer of this song, the sexy image can usually do a pretty good job of masking the not-so appealing reality underneath. I mean, I will occasionally take a look at some old Clinton picture, and still be shocked at how good looking he really was. Chubby, inflamed nose, baggy eyes, but the guy had "it", hands down. I think that had to translate with male voters as well. Of course, when you're dealing with someone who exudes sex, you can bet that he's exuding it on not just you, but everyone else (and their new blue GAP dresses).
But as you note, we usually only want sexy presidents after the un-charming one has bored us silly for four years - or maybe it's vice-versa. In the "modern era" - meaning televised debates/press conferences - you can probably successfully defend a thesis that the sexy presidents have a better chance at re-election, while the staid/folksy guys are doomed to one term, because we use them only for a quick four-year respite before heading back to Hef's Mansion. Ford doesn't really count given the way in which he was shoved into the job initially. Nixon maybe wasn't sexy, but again, by comparison he was (no offense to any of those who had it bad for McGovern - *shudder*). Of course, sexy also means shifty, glib, and able to lie with an absolutely straight face (Nixon: "I am not a crook!"; Reagan: "Iran-Contrawhat?"; Clinton: well, I only have so much space). This is the bad that goes along with the "good" of being tele-friendly and easier to relate to, and paradoxically, trust.
I mean, the boring guys are most always the much more honest (even with W, I doubt many think he's the one lying to us- heheh), but we either don't believe them or we don't pay attention because they don't have the passion to convince us to go along with them. It's a cruel reality that lying makes you a better politician. It's also no accident that entertainers make good politicians. G. Davis was/is a good-looking guy, but again, it's relative. He's going against Arnold Freaking Scharzenegger here. And Bustamente? Oh god. Once he crawled out from under the moss-covered rock that is the Lieutenant Governorship to stand up in the light of flash bulbs he was doomed.
Dean has that sexiness but in the creepy way some people fall in love with televangelists. It's not so much that women want to jump him, but rather that he can pack revival tents full of acolytes who want to give him their money. And that's what it's really all about: Money. And isn't that the ultimate aphrodisiac?