In 2015, my family and I did both the Halloween and Christmas party. For the Halloween Party, we arrived at our hotel (Contemporary, just to give you an idea of travel distance to the park) around 4:00, changed into our costumes, and headed to the Magic Kingdom.
That December, we stayed at Wilderness Lodge. We got up and had breakfast at the resort before taking the boat to Magic Kingdom. We got there right after rope drop. We had a dinner reservation at Ohana for 4:30, so we rode rides and such until we went to Polynesian. Then, we headed back to MK for the party.
Now, I do have a reason for posting both of those little stories. My family and I all agreed that the Christmas party went so much better. We got to take in multiple rides before the party goers were allowed in, which meant shorter lines than on other Magic Kingdom days. Then, for the party, we could enjoy the parade and fireworks, as well as more rides without really feeling like we missed out on anything. With the Halloween Party, we really didn't have part time before the crowd really hit. We didn't feel like we got to do nearly as much because we were choosing between our favorite rides and the party activities. I would recommend going to the park the day of the party, even if you can't be there for rope drop. Take in some of your favorite things before the party starts and then enjoy the party-specific activities. On my departure day, I'd do a fun breakfast (probably a character breakfast at Ohana, Chef Mickey's, or Minnie's Beach Bash) before leaving to go back to the real world.