We've been several times during the holidays. Here are my faves...
-Osborne Lights is a must for me...more times the better. I like going at least once right when the lights are turned on since it's cool to see and be in the big crowd for the ooohs and ahhhas. I like going another time towards the end of the night when it's quiet, as there's sort of a peace to it at that time. I like having hot cocoa during it since it kind of sets the mood. Oh...and make sure to try and find the purple cat.
-Resort decor is a must. Everyone has their faves, but the trees at the GF, AKL and WL are worth seeing. The gingerbread at the GF, Contemporary, BC, and BW are also a must. And if you like trains, YC usually has a nice display.
-The storytellers in Epcot are entertaining. So, if you already like going country to country, make sure you check the times in each country.
-Even if you're not doing MVMCP, you can still experience Holiday Wishes. In fact. you get a great view of the perimeter effects if you're outside the park. The Poly is the best place IMO, but the deck at the Contemporary and the dock at the GF are also great spots and all pipe in the music. Of course, if you're going literally right at Christmas, this will be your standard fireworks display. You didn't specify your dates, but since you mentioned MVMCP, I thought you might be going before the peak of the holidays since the party stops before the main Christmas rush.
-Illuminations has a holiday tag at the end, so make sure you see that.
-I love all of the park decor and trees, so make sure you cash in on those photo ops.
-Dreamlights- end of story
-You'll find there are some seasonal treats and drinks...so try those as well.
-If you have time, head to Ft. Wilderness to see all of the decked out campgrounds and maybe do a sleigh ride.
-Santa...I think he's in DTD. DTD also has nice decorations and last time we were in DTD during the holidays, they had musicians out playing classical Christmas music.
OK- that's all I can remember right now.