Before you decide whether or not to do insurance for the trip, you might want to check out your health insurance policy. Does it cover you out of the US? What about a medical evacuation? My point is that SOME medical policies cover these items, some don't. It's not just a matter of what company your insurance is with, it is a matter of your policy. It's no difference than some medical insurance covers prescription drugs, some policies don't.
A helicopter evacuation from the ship can cost as much as $25,000. Admittedly, the chances of needing this are small, but wow, that is big bucks. It is less to be evacuated from one of the ports of call, but still major $.
You might be able to lose the cost of the cruise, but what if you needed that medical evacuation? Most
travel insurance covers things like uninsured medicals, lost luggage, emergency evacuation, etc.
You can get private policies for travel insurance at significantly less money than thru
DCL. Also, they will cover your whole trip even if you booked air separately or did separate land/sea trips (whereas the DCL will only cover what you booked thru them). There are 2 mistakes you can make:
The first mistake is to get insurance and not need it. IN that case, you are out a small amount of money--maybe 5-10% of your trip cost.
The second mistake is to not get insurance and need it. In that case, you will be out at least the cost of the trip, and maybe a very lot more.