Best strategy for MK/WDW near Christmas

[dizzyinwdw]

Currently booked to be at WDW Dec 18-24. Planning to go to 3 parks (DHS/MK/Epcot). Trying to decide if it is better to buy 3 day MYW tickets OR stick to 2 day MYW tickets and buy tickets to MVMCP. We have never gone to WDW at Christmas time so we are not sure of crowds. Is the party enough time to do MK? "Must dos" are 7DMT and A&E (if available), Buzz and the parades/wishes. Or should we do a full park day at MK (Dec 23)--How are the crowds Dec 23? Kids usually don't last a whole day, so I am thinking of maybe splitting MK over 2 days (one morning-early afternoon/one late afternoon to close). Should we worry about not being able to get into MK on Dec 20/21/22/23 evening due to crowds if we do a split visit? Cost is approx the same for 2 days + party vs 3 day MYW, BUT if we decide to go for an extra park day (maybe AK? or extra MK day plus party) it is cheaper to do 3 to 4 day MYW ticket upgrade vs 2 to 3 day upgrade. TIA!!!