Hi, Janet!
Mickey's Very Merry Christmas Party is one of my favorite holiday traditions. I love the snow on Main Street, the free cookies and hot cocoa, the beautiful Cinderella Castle Dream Lights, and the amazing fireworks.
While the party officially starts at 4, historically they will let you enter sometime around 4pm. To make the most of the party, I suggest getting into the park before 5pm, grabbing an early Quick Service dinner, then get ready for the festivities! Make sure to get a Times Guide for the party so you know where to find cookies, where the dance parties will be, and what time to be ready for the parade and fireworks. Bring your camera for some wonderful holiday photos - almost every year we snap the best pictures for our Christmas cards!
If you have the time and the extra money in your budget, I would definitely go! If you are a bit worried and want to skip, make sure to at spend a non-party night at the Magic Kingdom so you can enjoy the Castle Dream Lights. It is a sight you will never forget!
Whatever you decide, have a wonderful vacation and very Merry Christmas!