Does Disney Raise Dinning Prices During Christmas Week ?

They must because last time I went was about 2 1/2 years ago and the price for an adult at one of the buffet restaurants was
around $28.00.

We just got back from WDW a few days ago. We ate at 2 buffets, Crystal Palace and 1900 Park Fare.
The price for an adult was $39.99 !!!
I couldn't believe it.

Neither one was worth $40.00. I would rather gone to a nice restaurant instead.

Short answer? Yes. Disney began adding seasonal surcharges to buffets, character meals and such a few years ago. Typically it's around $4 OOP per person plus tax & tip.

Note that this is not just around Christmas, though. They also tack on these seasonal surcharges during the busy summertime period as well as other peak travel times.