I was just in St. Lucia for a couple weeks and wanted to post so others had some more recent info. I have been kiting two years and am not affiliated with anyone.
Spot: Kited in the South at Anse de Sables. It is nice bay with sideshore breeze. The water was reasonably choppy. It was fairly windy while we were there usually ~ 20-24 knots. Swell comes from the north and east resulting in a funny cross chop as you get further out. The inside is smoother with some nice rollers but no real rideable waves. The outside had up to chest/head high rollers from two directions intersecting as described above. There are waves out on the reef but one set is in a wind shadow and the others you cannot get to because of the airport restrictions. The bay is curved so that it is more onshore as you go further south, good for beginners.
There were 2-3 average windsurfers and 2-3 kiters out in a large bay, not crowded at all. On Sat and Sunday alot of St. Lucians came out which was cool. Rastafarians with their horses on the beach, but not enough to impact kiting.
We heard the bay up North at Cas en Bas was smoother water, with waves on the outside reef, but was much smaller.
Wind: Kiteable every day for two weeks. Rode mostly 12M. one day 15M, a few days smaller kites. Folks the weeks before rode 12M almost every day. Somewhat holey due to islands outside the bay, an occasionally gusty as systems rolled through, but not bad.
Accommodations: There are the Reef Beach Huts which looked alright, simple, clean. We stayed up on the hill in a guest house which was nice, but we didn't like having to pay to get taken to the beach every day. We heard Labadie's apartements were a good place to stay.
People: The folks at the Reef were super nice, but they are not kiters or windsurfers. They run the restaurant. They are good folks who run a animal relief society and there are lots of dogs and cats around. They were very chill. We had nothing but good interactions with the St. lucian's. There was reports that the group before us kited a few bays up(where Ten 4 was filmed) and had a knife pulled on them, but the guy ran off). We had not issues at Anse de Sables.
Food: Pretty limited. The Reef had reasonable food and milkshakes, but we were a little tired of it by the end. Best bet is to get a place with fridge and load up the grocery store. Eat dinner at The Reef or drive someplace. There is a KFC in town and a big grocery store.
Lessons: I did not take lessions but there were alot of people who did. Overall the kite instructor seemed nice and knowledgable(they change often though, so probably we worth checking if you are counting on lessons). They had nice boards (North series) but a moderate/poor selection of kites, particularly the smaller ones. The smaller females I talked to were frustrated by the lack of appropriately sized kites for them in the prevailing conditions. If you can bring your own gear definitely do.
Transport: We would advise to stay close to the beach, or to rent a car. We found getting transport from our guest house a little frustrating as we wanted more freedom.
Nightlife: Pretty much nonexistent. Just not alot of people there. I was cool with it as I was beat from kiting, but this is not Cabarete. Very very chill. If you want nightlife the North would be much better I think.
Exploration: On the drive out of the South we saw maybe 3-5 mangrove like bays with flatwater inside, ridable waves outside. If somebody hooked up transport to those places they would be much better for advanced riders than Anse de Sables.
Overall: If you go to St. Lucia definitely bring your kites. I had a good time but was a bit dissapointed with how choppy the water was and the lack of ridable waves where we were. Still kiting every day on small kites was great and it is hard to complain about that.