My friend does in-home boarding and rescue, and ironically the dogs who are vaccinated actually seem to get it more. I believe it's like the flu shot - the kennel cough covers a very small percentage of the strains out there, so it does nothing if the dogs are exposed to one of the other strains.
Meg's never had it, but a foster I had before her did. Basically you let it run it's course. I wound up getting cough meds from the vet for her, because it was keeping both of us up at night.