What is the weather like in mid to late December? Is it worth going this time of the year? I don't like being cold and I wouldn't by any means like to hike through snow. How likely is it that there is snow at the South Rim this time of the year?

More than possible

We were there last week and it was in the teens to 20's at night. The daytime highs were in the 60's and 70's. December will be a lot colder and there will be snow. I'd suggest waiting until at least April.

Not sure about December. But I will tell you that what a beautiful site it was in October. We just back from going to the South and the North Rim. It is well worth the trip. I would call there hot line. Have a great trip.