Well since I'm in the Holiday spirit, I'll give the "right out of the cast member's mouth" facts. If you want to spend New Years eve in one of the parks remember this "GET THERE EARLY". For example be there at opening or an hour before.
For Chirstmas eve, Xmas, New Year's eve, New Years day - The parks are all expecting full attendance.
The crowds on the off days leading up to the main events tend to only really hit high amounts in the late afternoon. For example, MGM really starts to pack them in after 3 pm. So if you get there at opening, you could have everything done (but S of Lights) before 3. Epoct same thing, the only chance of getting a good seat (like not standing) is if you are the dinner package.
So the holiday theme this year is Get there early!
Hope this has helped, this is the greatest time of year to come to the parks!
PS Go on star tours and look for the guy with the lightsaber, you may just find Vash....
Enjoy your trip!