Moonlight Magic does not come out of our annual dues. You can look at your annual dues budget to see where the money goes, none of it goes towards events such as these.
You're right in saying new points for sale may be more expensive as a result of Moonlight Magic, but if you don't buy anymore points - you aren't impacted by this?
Moonlight Magic is funded by Disney Vacation Development which is the entity that sells points and is part of their marketing budget. It is a way to help entice new buyers to buy direct points from them (e.g. Guides can say: "If you buy points from us, you qualify for Membership Extras which includes private events called Moonlight Magic!").
Last Moonlight Magic I attended, they also introduced a "bring a friend" in which they gave you free luggage tags in exchange for signing your friend up to learn more about
DVC.