I am very married to the d8; it fits them much as it fits a monk, rather than as a standard cleric (where, really, there's no especial reason why it does fit other than the fact that they fight a lot, which really isn't a reason why you would be healthier, just a reason you'd be glad if you were). Going Charisma for casting would resemble the Favored Soul too much, plus it would imply that they're kinda superficial if they're no longer required to be Wise, and that's an impression that's too easy to get from them as-is. They may come across as being lovey-dovey, but they're serious business; I can live with them being a little Mary Sueish rather than even the slightest risk of them coming across as shallow, vapid, or a joke.