Ooh I like that concept of Ben turning up and helping the Scoobies. Especially if both sides remain clueless. But with Glory being a good guy and all and presumably wanting to consider her little group would she confess to them her Ben weakness? So they know there's always that risk? Or would she be too ashamed and worried about what they'd say that she'd keep it secret?
And as for Spike knowing about the transition I always presumed it was because at that point Glory's spell was starting to weaken and people were beginning to remember. Like at first NO ONE remembered, and then just non-humans such as vampires until eventually the rest of the gang remembered too. I may have interpreted that wrong though....but if we did consider it that way then that would mean we could keep Spike as clueless as everyone else.