It is a GREAT time to go (early December). It is definitely a 4/5 time period vs. 2/3 (that is a joke). You get Christmas, close enough to Christmas to feel Christmassy...without the INSANITY that is Christmas at WDW. Really, wall to wall people. During this time, ADR/FP+ can be challenging to find, but they are findable. Waits will be there, but just be smart with recommended park days/etc.
We went to the 12/10 party last year...and I didn't realize it was a sell out (part of me doesn't believe it was). We bought our tickets last minute, and the CM at BLT didn't think it was close to a sell out, who knows...I am someone that says she will NEVER go to a sell out party, and well, maybe I did...and enjoyed it! We were planning on second parade, but then my inlaws legs started to ache (we were at MK all day), so we squeezed in with some nice folks in Frontierland (they invited our two boys to sit up front with theirs). FWIW, the 12/10 party was one of the most recommended dates (least crowded) predicted for 2013. Who knows.
Here is a link to wait times for a sold out party...and it looks pretty good.
http://www.easywdw.com/uncategorize...-sold-out-mickeys-very-merry-christmas-party/
Don't forget to pick up your SOTMK Elsa card! Even if you don't play the game, the cards are GREAT free souveneirs, and the Elsa cards are selling for over $30/each on eBay, if you really aren't interested in them. My boys love collecting the cards/DS8 plays the game.
To recap, it is an awesome, AWESOME time to go. You will love the Christmas stuff (if you want a minnie green/red ears, buy now...they were sold out when we were there). Crowds will be there, but not scary. Take time at night to stroll the boardwalk area, popping in the YC/BC and BWI to look at decorations. If you have a car, head to WL and sit and play some cards in the lobby (buy a coffee/beer), and soak in the tree/decorations.
One of our favorite activities at the party was the encountering The Rusty Cutlass Band (singing/bell playing pirates). Just a bit of Christmas sweetness. The parties (including the apparently sold out ones) just slow things down in the parks. There are so many rides that are different/more fun at night, and with slower waits, you can enjoy them all (BTMRR, AstroOrbiter, Peoplemover, Speedway, Dumbo/Carpets, Jingle Cruise).
No frowny faces allowed...reserved only for those who don't have a WDW trip scheduled : (