Try explaining to an undecided voter that a campaign commercial with a pretty white woman is secret racist code that says Obama is a lecherous black man who wants to bang white women. The undecided voter will think the left is paranoid and they will want nothing to do with us. Sometimes what looks like a vapid juvenile campaign ad is just a vapid juvenile campaign ad; it doesn't necessarily have any hidden racist signals. When Republicans call Obama adjectives they routinely call other Democrats (elitist, presumptuous, etc), it's not suddenly racism when they call Obama those things. We should stop acting like it is.
"Dog whistle" has become a very overused phrase here, and we should let it go. It's really bad campaign strategy to call Republican attack ads racist, if they aren't clearly racist. It makes it look like we're the ones who can't win the argument so we resort to name calling. Any effort we make to explain to the masses how a seemingly innocent campaign commercial is coded racism, is an effort we would be better off using to explain to the masses why they should support our liberal positions.
The purpose of dog whistle racism is to tell racist voters that they should vote for you, not the other guy. You don't need it if you are running against a black guy, then the racists are already going to vote for you. It won't help you win voters who weren't planning to vote based on race. The Republican campaign isn't using dog whistle racism, because they don't have to.
Of course we should speak out if we see overt racism. For example, the Texas GOP gave out pins that said "If Obama wins can we still call it the White House?". We lose credibility to criticize actual racism if we also try to claim the Celebrity ad is racist.