“Yes, but how does “excitement” change the quality or quantity of the pool of candidates.”
Because the voters were more familiar with Palin than Bachmann, Cain, or Perry. They may not have bothered to listen to them much, hoping that Palin was going to be running. Her daughter said last summer, that her mother definitely knew whether or not she was running. No one would have cared about “Undefeated” or some of her speeches if she wasn’t going to be running.
Again, how does this change the pool of candidates. If your definition for harm is minor changes in the dynamics of the race, which is obvious, then you're not really saying much.