You do not have to insure "the total cost of the trip" (though perhaps you do if you paid for it as a package--I don't know). I rarely do. If you are paying separately for airfare, lodging, land transportation (cheap in C. America), national park fees, and the liveaboard, you could insure a lesser amount. Airlines typically let you cancel and rebook for another date, so I don't bother insuring air tickets unless the destination is truly likely to be a once-in-a-lifetime for me. Lost baggage--again, there is some compensation from the airline, and homeowner insurance might also cover some surprising cases of lost/stolen personal property, so check your policy if you have one. Lodging I rarely pay for in advance--at most I have given a deposit I am willing to lose if I have to cancel--so I don't really need insurance to cover that. I tend to insure only big items I have paid in advance for. All in all, I try to keep in mind that the risks we're talking about here are low, and that's why there is no shortage of companies happy to sell me travel insurance. By the way, travel insurance that includes medical coverage is often based on the insured's age. A quote for the same policy might be significantly more for a 60 year-old than a 30 year-old.
You mention "repatriation" and I assume that means evacuation to your home country. I try to keep in mind that even in Central America there are good treatment options for many medical issues. I badly sprained an ankle in Guatemala, and I went to see a specialist doctor. Seeing the doctor, getting a brace for my leg--all cost me something less than $200 out of pocket. For sure, there are pricier medical treatments that I wouldn't want to have to pay out of pocket, but my point is that the probability of needing to be evacuated to your home country for emergency treatment is low. That said, DAN's upper-tier "Enhanced Membership" that currently costs $75 (that is membership, not the optional accident insurance) includes up to $500,000 in emergency medical transportation.
A liveaboard is a different animal, and there are many many threads discussing how different people approach insuring against the various risks involved in a liveaboard booking. Depending on the reason for cancellation or interruption of a liveaboard trip, the company might issue a voucher for a future trip, like airlines do. One interesting SB thread I can recall discussed a situation in which the liveaboard simply decided to cancel its trip because too few people had booked. The liveaboard offered some lame options as compensation. The diver's insurance did not cover a company simply reneging on its obligation to conduct the trip. In cases like that, a diver's recourse is presumably to sue the liveaboard company for breach of contract--something probably not practical. Reading these threads, one can become jaded and decide insurance doesn't cover the things that most concern liveaboard divers. Still, if it's a pricey liveaboard the cost of insurance might look reasonable. There are ways to try to mitigate risks involved in liveaboards (and other cruises), such as arriving at the port city a day or even two days in advance; if your luggage doesn't make it there with you after a flight, it might catch up with you before the liveaboard departs.
For dive-related accidents, DAN is very popular, as you know. But it had been pointed out in various threads that more general insurance may in fact cover the same things DAN or DiveAssure would. Who knows for sure until a claim is made. DAN has the hotline, and it has been discussed whether they have a special mojo that other insurers might not to smooth coordination among different parties in a dive accident evacuation/treatment situation.
It's also possible to buy medical-only insurance instead of general "travel insurance." Maybe you decide you can handle out of pocket the risks for trip cancellation/interruption and other events of the type covered by general travel insurance. I have used GeoBlue for travel medical, based on my understanding of what my US medical insurance would not cover. Others have said their US or Canadian insurance covers them well enough on trips abroad that they don't feel they need separate medical insurance.
