I'm completely uninterested in the crossover character deck, but figure that if it brings up the game on the radar of a few Sentinels players the extra reach can only benefit. This kind of KS lives and dies by its reach - not a lot of individual backers will go above ~$70, so the primary way to reach higher is getting the word out to more people.
Of course, they can't water it down by adding a bunch of crossover/non-Dresden stuff, but one character among 13 if we reach Mouse (which I have no doubt at all we will do) isn't really dilluting it much.