Just for future references, I would call instead of fax. I'm not sure how they do it with fax, but when you call, they can give you an amenities confirmation # over the phone. Often times, they will email you the confirmation right away and will even stay on the line with you until you receive it.
We did Xcaret in Cozumel, Mexico. Loved the resort. Loved the cenotes. But the bad part is, there simply NOT enough time to really enjoy the resort. Still, I would do it again, but I really wouldn't mind a few days there. The food was mediocre, but still enjoyable, but at least it was included while we were there. I would keep an eye on any security warnings from the State Dept. Of course, zika was the big hubub when we were there. Nowadays it's security warnings, but that's been lifted.
Grand Cayman was our least favorite port. We actually enjoyed the tendering, as it was something different, and it also posed great photo ops of the ship with it being further out from the port. We really struggled with excursions in Cayman. We didn't want to just lounge on the beach. Didn't want to snorkel since we could do that on Castaway Cay for free (though it's a very different experience, and one that may be more worth it for you to do an excursion in Cayman for instead of just CC.) We ended up at the Turtle Farm, and it was ok. We did do a bit of snorkeling there, and the whole place was interesting and neat, but just ok. Better than paying for just a beach experience, but not as exciting as other excursions.
Falmouth, we really enjoyed. A LOT more than we thought we would. We did the shark encounter, ending up in Dunn River Falls, and loved that. We fed, held, snorkeled, and swam with the sharks. Held some stingrays, parakeets, and iguanas. Sampled coffee, and rum. Ended the day hiking up Dunn River Falls, which was a LOT of fun.
Castaway Cay, in the past, we've done the feed and snorkel with stingrays excursion, which we did enjoy, (and part of the cost goes to Disney's Conservation Fund) but didn't do any excursions there on our Western Caribbean trip. We'd done an excursion in every port up to then that I just wanted one day of nothingness, just relaxing, and going with the flow. It was really, really nice to just go at it slow, at a leisurely pace, doing whatever, or nothing at all to relax before having to return back to the real world.
All of our excursions included lunch so we didn't have to worry about that, so that was nice.