I cannot think of anything more magical on Christmas Eve than the Candlelight Processional. It was truly one of the best things I have done anywhere, in or out of WDW at Christmas time.
We have been that time frame (well actually coming in on the 26th to January 8) and it is extremely crowded. However, we did get quite a bit done and we are not morning people. Most days we didn't get to the parks until late afternoon. We just went knowing that for major attractions the fastpasses would be gone and the waits not worth it. So we did things that don't have long waits, the shows, the parades, TTA, COP, things like that. We also did the EMH at MK one night until 4:00 a.m. By 1:30 we had the park to ourselves and it was heaven. I must say exiting the MK at 4:00 a.m. was a bit surreal. I highly recommend Tour Guide Mike. He has a holdiay survival section and even though I have many trips to WDW under my belt, I use him every time. By following his advice, we never encountered a park closed to capacity even though it did happen during our stay. We just knew which parks to go to on what day. ADR's are a must and be aware that having an ADR will not guarantee your entry to a park if it is closed. Even something prepaid like a CP package. So do make sure you either get to parks at opening or use a TGM or UG type plan (I prefer TGM) to help you make the right choices.
I say its a wonderful time to go. I was glad it wasn't my first visit and that I knew what to expect. But the long hours, lovely decorations, ambiance and our realistic attitude about what we would be able to accomplish, made our trip great. I hope we get to go again someday and I'll want to do Candlelight Processional on Christmas Eve for sure when we do!