Rahul Gandhi's charm is already much talked about. Here's some evidence of that.
Rahul Gandhi on Raj Thackeray
Charm by itself is probably not something to vote for. But Charm + intelligence + vision + dedication + a will to better the lives of his countrymen + a liberal outlook, well that's a good combo to vote for I think. (For now I am ignoring Rahul's recent publicity hogging over the Vedanta issue, which was a bit of a let down). Charm and charisma I am sure play a role in diplomacy too. Too bad Priyanka Gandhi is not too interested in politics.