I am sure lil99 will chime in with more, but my wife and I took our 4 year old last December, and here is what I'd say...
So...it might depend on what the promos are, but we leveraged every after-hour opportunity to the last minute and rode lots of things. Our four year old hung on like a champ until after midnight some nights, and as a result got to ride a lot of rides multiple times.
- Deluxe was worth it to us because there were a couple of nights that had extra park hours (and lower crowds) if you were staying at a deluxe resort. One night was Magic Kingdom and one was Epcot. We stayed at the Boardwalk and it was cool at Christmas. (If there is no promo like this, it might not be worth it.)
- We also spent money on the after hours Christmas party at MK one night. Again, worth it for lower crowds and extra hours. Also recommend this because it gets you to MK on a day when you can go to other parks during the day or even work a rest day in with the party that night. (Do Epcot the day after this if you can since it opens late.)
- The after hours things (if available) make the hard to come-by rides much more manageable. Things like Seven Dwarves, the Frozen ride, etc, are much easier to make happen (sometimes multiple times).
So...it might depend on what the promos are, but we leveraged every after-hour opportunity to the last minute and rode lots of things. Our four year old hung on like a champ until after midnight some nights, and as a result got to ride a lot of rides multiple times.