Just a quick follow-up:

1) For Cozumel, we hired a cab through Eduardo Esquer. Although Eduardo was not our driver, he had one lined up for us who took us around the island, including to the San Gervasio ruins, a beach on the south end of the island, and some shopping. While the taxi service he provided was perfectly fine, I think he was only necessary for transport to San Gervasio and back - the other places had cabs coming by, and it would have just been cheaper to hire them as needed, or even renting a car on our own.

2) For Belize we booked a tour through the cruise line because I couldn't find an equivalent tour of what we wanted to do online. You do get a slightly higher priority with the tenders if booked through the cruise line which may be better for ports with shorter stays like Grand Cayman.

3) We booked a kayak and snorkeling tour through ShoreTrips.com in Roatan. This excursion was fantastic and I highly recommend it. ShoreTrips is a third-party booking agency and the actual tour was run by Subway Watersports - however the price is identical booking with them.

4) We had nothing prebooked for Grand Cayman and after seeing the docks at the previous places, we determined we could easily find an excursion of our own upon arrival. Unfortunately the other half wasn't feeling too well that morning so we just showed up around 1p and wandered around town for a few hours.

Cliff Notes: I was quite happy with the results I had with booking outside of the cruise-sponsored ones and recommend others do the same!