We saw all the Christmas shows on Christmas Day 2015 with the reserved seating package.
But, as FLOIR mentioned, we had no time for the Fireside Feast (which is an awesome experience) and no time to truly enjoy the Christmas Pathway. Last year, they introduced Rudolph's Christmastown which was very well done (meet and greets with Rudolph, Clarice, the Bumble, and Yukon Cornelius) which you would most certainly miss if you had only one night at your disposal. To enjoy all of the Christmas Celebration events and attractions, you most certainly need two full nights.