We were considering MVMCP also for this Dec. and decided against it.
We just went down to WDW in April, and despite my best intentions of making it to all of the night shows, after going to Spectromagic and Wishes on the first day at WDW, my DS3.5 and DD1 were wiped out for a couple of days. At home, both kids usually go to bed at 8 p.m. and they just can't handle doing a half-day and a long, late evening at the parks (we stop for nap/swim breaks in the afternoons).
Plus when I looked at what we would get for the ticket price, it was basically a parade, fireworks, a photo, cookies & hot chocolate, the ability to ride the rides until midnight (which we just wouldn't be able to do), and the extra magic. We decided it would be much more magical to get our rest and be at the parks for opening time the next morning. We'll hold off on MVMCP until our kids are older and would enjoy it more.
But really each family has to decide based on itself -- if you think your daughter would enjoy it, then I say "Go for it!" If not, spend the money on something else she would enjoy.