For the ports of call that you listed I would say that water shoes aren't necessary. However, they are cheap, and don't take up any space in your luggage or your beach bag. If the sand is hot…put them on; if there's rocks or coral…put them on. I do take them with me just in case it becomes a necessity to wear them.
Yup, they don't take any room to speak of in the luggage or in the beach (canvas) bag that we all seem to lug with us when we go ashore. I like to have them along and I wore them on a kayak excursion in San Juan because they were better option that going bare foot.
WOW! I've never been barbed by a stingray yet. Thank God! I did wake a huge one up once that was sleeping in the sand at Trunk Bay. I ran out of the water and told the Lifeguard. He told me I just woke it up and startled it, and to shuffle my feet when I'm the first one in the water. I didn't know they could get that big!
The wing span on the one that nailed me was about 6', guess it was a baby. I know I startled it when I stepped on it, but I didn't know it was there. They have fantastic aim with that tail. About 9" of barb stayed in my foot/ankle area for 7 years. Then it started coming out in pieces, by itself. Finally, I went in and had as much as the surgeon could find removed. He still didn't know if he had gotten all of it.