Don't want to be difficult but only you can determine need (and risk). We have taken about 10 cruises over the past decade and haven't bought insurance for any of them. We have had two incidents that required a trip to the ships doctor. The first was about $200 which we covered out of pocket. The second was covered by
RCCL as it was an accident that happened on a ship excursion.
However, our health insurance covers us for out of country 'emergencies'. Of course you would have to pay and then file a claim. The grey area would be if a medical evacuation off the ship was required. There are insurance policies you can buy that just cover that and/or repatriation. Might be worth looking into.
In any event, definitely worth speaking with your Health ins. to see exactly what they will cover and be very specific that you are going on a cruise.