I would disagree that the other guests stories/arcs don't develop much, in fact i think part of what makes the show so brilliantly written is how much they do develop in the lyrics and songs as the night progresses. But in many ways the development is learning who they are and were, rather than a plot of theirs developing, all as related and seen through how their experience of the party on this night progresses.
I can't argue with the Mandy similarity though... however I do think he's great in both, but in WP he gave one of the most astounding performances I've ever seen in a musical.
