For Goofy's Kitchen, the price most certainly goes up during peak seasons such as the holidays. In fact, the breakfast and dinner prices can jump by a full $5 - $7 per person in peak season. I can only assume that Ariel's Grotto (because it is considered Premium Dining like Goofy's Kitchen is) raises their prices with the peak seasons too, but I could be wrong on that. Surf's Up with Mickey and Friends is all-buffet, so I would imagine they would raise the price as well. Not sure about Minnie & Friends or the Critter Breakfast.
I have no clue about the regular table service/non-character meal prices. Good question.