I think the swirling skirt thing is over-rated!
The winds can be strong and you can end up struggling with your skirt all night! So for sure wear SOMETHING under that skirt or all of San Pedro will see what you have to offer!
I also agree with no High Heels, there is hardly a flat surface anywhere on the island & twisted ankles and skinned knees can be common! Perhaps you have some romantic shoes with tie straps!
Also if you take a boat to get to dinner you might want to prepare for any weather conditions, of it is windy & rainy some of the daywear is a little flimsy for the natural elements! I prefer capris, a sexy top and comfortable light weight shoes for a night out. Barefeet can get hurt on glass, bottle tops & coral rock, and nighttime is easy to step on some! Enjoy where ever you go & what ever you eat!