I think Disney has decided to 'cash in' on the after hours parties!! A ton of people go to them, they pay in the neighborhood of $40 per person to go. So, Disney started the Halloween party earlier in the year, way into Sept. Started the Christmas party earlier in Nov. So, I'm not at all surprised they have come up with a new theme party to part us from our cash!!! Now, I have been to
MNSSHP, to
MVMCP 4 times....and I'm going to the Pirate and Princess Party on Jan 26, so they get plenty of my 'party money'. I'm not complaining. It gives me 5 extra hours in MK, which for my family, is priceless, or at least $40!! This time around we have only the one day in the parks, so we get to do our favorites in Epcot and AK and then head to MK for the after hours party.
No one knows yet how crowded these parties will be. The other parties can be very crowded, but it's all relative. If you are used to going in mid-Sept and being able to just walk on any attractions, then you are going to find the parties very crowded. I've been at Thanksgiving, early summer, mid summer, early Dec...so it's only a little crowded to me.
Is it worth it? That's up to the individual family. They do have a set number of tickets to sell, and some parties have sold out in the past. The number of tickets for sale is huge though, so you aren't going to feel like you're alone in the park.
As someone else has already said, they most likely won't have it in Dec..they already have the MVMCP then, they don't need another one. Perhaps they'll come up with a different theme for the 'warmer' months.