I have been thinking about this more then it probably warrants, but a couple of things popped into my head, maybe you have an answer or two for me.
1. Since this is a one night event, how much does it cost Disney to produce? With an event like MNSSHP they can spread the entertainment costs over multiple parties to decrease per night expenditure. But for a one night party, they need to take entertainment CMs and train them and rehearse, and build sets and costumes, all for one evening. So the cost must be higher. Which is maybe why they sold unlimited tickets?
2. Why is this only one night? Why not run this from say, now, till the end of September once a week? Spread out the costs, lower the guest cap to a more reasonable number, and have more, happier customers?