Nice in December

Just do it.
I go to Europe most years over Xmas break from academia. The days are shorter but it is interesting to see Xmas lights European style. You can easily do a lot of daytrips from Nice to places like Antibes, Eze, Monte Carlo etc.

It sounds like it would work for you, but be aware that a lot of sights in that area are closed multiple days a week at that time of year. Some will only be open 4 days a week, or perhaps even 3. It will be very important to check websites carefully for current winter schedules if you want to go to museums and other indoor attractions.

There should not be a problem with sites and attractions in the city -- really the only impacts will be operating hours might be trimmed by one or two hours in the winter. In December in particular things remain open due to Christmas, the Christmas market and the extra foot traffic of the holiday shopping season. The only things closed are seasonal business (water sports, boats, beach provision shops for tourists, beach clubs and a few random businesses). If merchants are taking their holidays, they tend to do it January or November.

Thank you everyone!