First of all, if I was pregnant or likely to conceive, I would probably not to the Zika areas right now, at least not for an optional vacation.
I am not advising anyone not to be worried about it, but I am not worrying too much about it. While we lived in Asia, we spent many years vacationing in Thailand, Singapore, Malaysia, Borneo - at least 2-3 weeks a year. DH was frequently also in India for work and we lived in China. These areas have widespread Japanese Encephalitis, Dengue Fever, Malaria (and that is just the mosquito borne illnesses..!) We and others traveling and living there didn't take the situation lightly, but you learn that mosquitos are not out on beach areas much during the day. I don't ever remember any bites. We had young children. I was even pregnant and youngest Ds was borne and grew up there. During Early Morning and Evenings, one has to be more careful, also in jungle and rainforest areas. The chance of getting bitten mid day on a beach or snorkeling trip is not very good. Thus, in the Carib I would be very careful especially in the evenings, BUT on DCL we won't even have the opportunity to be on the islands during early mornings or evening. The port times are too short.