I have stayed in Curry Village in the winter. As the park does get snow if you plan on camping you will need gear that can keep you warm at below freezing temperatures. There are some trail closures in the winter, notable the mist trail since it becomes very dangerous with the formation of ice. Food in the valley can be hit or miss, as it is in the warmer months. The park store does offer reasonable prices for basic food stuffs if you don't feel like eating out. Depending on the direction you come into the park you might need snow chains/cables. The higher passes are not plowed in the winter.

Once in the park to make the most of it i recommend getting up before the sun. In the winter you don't get that much sun light into the valley. But what you do get in low light that is great for photographing the park. The valley takes on a much different character in the winter months, frozen water falls and rivers, the meadows are made softer with snow. Its well worth a trip.