We have been a few times at Christmas and was there last year too.
The Townhome we stayed in did have a Christmas tree which the owners said we were more than welcome to use, as long as we put it away before we left. We have bought a small tree on previous stays from Walmart or Target.
Last year for Christmas Dinner we went to Whispering Canyon cafe at Wilderness Lodge. It was a "Holiday Meal" and we all really enjoyed it. We have also been to California Grill a few times (and seen the fireworks too), Citricos and Cinderellas Royal Table. I suppose it depends what you want and how old your children are.
Last year was the first time we have stayed for New Years Eve and we ate At the Yacht and Beach club and then enjoyed the outdoor DJ. They gave out hats and party blowers and there was a good atmosphere. We also got to see fireworks from Epcot and the Studios which was pretty good. Leaving the area wasn't too bad either but it is pretty busy and if you go to a park I can well imagine it will take a while to get back.
If I can answer anything else let me know