Tell that to Dan Quayle, a bright and attractive candidate who was basically marooned on a desert island after Bush I lost the 92 election.
As far as I can see there is no basis in fact for the popular caricature of her. The gulf between the myth and the reality is so wide that the she may actually benefit from all the abuse heaped on her head. A presidential campaign is likely to make her most passionate critics look like the buffoons they are and give her an opportunity to sail comfortably over a very low bar.
At any rate we had all better hope Palin can overcome her liabilities because, for better or worse, she's likely to be the best we can find for 2012. I'm open to alternatives, but I don't see any.