This is pure speculation on my part, but the primary reason the US is involved in Haiti is to prevent an even worse crisis than is already happening, thus preventing an exodus of refugees fleeing to the States. So in that sense, it is in America's best interest to bring back stability to Haiti.
And, slightly off topic, I just know that there's going to be some movement for the invasion of Cuba, just like there was after the invasions of Afghanistan and Iraq, but that'll never happen.