I have been night riding since I started kiting. It seemed pretty natural since I use to windsurf at night. Lack of light seems like a fairly minimal deal, at least to me. Other things that you mentioned concern me more and I agree, should be taken more seriously as threats.

Odds of sharks I think is your question? So small as to not be worthy of consideration, especially in FL. It never even crosses my mind. Odds of losing your board if you get tea bagged? (less likely with today's kites) Fairly high.
Obviously limited sight has a few drawbacks. But, if you know the area, it's not that big of a deal, imo.

Probably the biggest danger with night riding is getting your bar backwards or having a bridle tangle that you can't see. This is especially a problem during launching. Not being able to see the problem is a problem.
Self launching at night is a real treat

Lastly, if you get hurt, people can't see you. There aren't many people out where we ride at 10pm or even midnight, sometimes.
Probably the biggest thing I worry about are the people themselves in a couple of the places I ride at night (who is walking around at midnight?)

Anyway, I have at least 70 night rides in the last 8 years and have not had an incident (well, except the time I landed on a Land Rover, but that was my very first night session and I was a newbie).