I am not a "long time nudist" since we only started at CSS in 2008, but I can answer a couple of questions. We always go early December - hurricane season is over, and the rates are still down. The pool can be a little chilly, but not to bad, just like southern Florida would be I would guess. Socializing is great. There are plenty of people who go early December, and use SSB. I never saw it as limited. I don't know how many of them use nudist facilities in the states (we don't really have any near us- and there is only a couple of months that we could in Wisconsin), but I would think the attitude and feelings of "newbies" at CSS would be similar to any longtime nudist. Also, at that time of the year there is many repeaters that go to CSS. Go and relax. I am not sure you would even know who is a "newbie" or who is "seasoned" unless you ask or they tell.
We were there Dec 3 to 13 last year. It was in the 80's everyday. It was fine for us since we live near Lake Tahoe. There were more people at SSB in Dec than there was in May 2013. We will be there again in May and Dec 2014. This year our travel dates are 10th to the 21st of Dec. Hope to see you there.
We started out at Tower Isle many moons ago it seems and since then we've become "experienced" and have been to 4-5 different places in California, a handful of places in Florida and we have our "place" in our home state and even participated in the World Record Skinny Dip last summer. We're way to the younger end at every place we go although every year we get older and I can honestly say that even though some of the resorts were very nice, the best place that we have been is Couples Sans Souci and more specifically Sunset Beach. Whether there's 20 people there or 50, the people are always very friendly and we've made friends that we keep in touch with and have visited clear across the country. We were at Tower Isle for Christmas years ago for our first visit and there were tons of great people on the island and the water/temps were plenty warm (heck, you're getting closer to the equator) so you're in for a great visit.
The only thing that may bug you as an "experienced" person is that many people don't understand the importance of towels to the nudist lifestyle and you'll see people sitting on chairs without one from time to time and that's just wrong. We typically get a lecture (because of our age) even at places we've been before about always using a towel and I just smile and nod like I'm clueless.
Have a great trip, although after going to SSB your other places to go A/N are going to seem crummy