ALWAYS buy the travel insurance
Look, no one wants to cancel a vacation. No one books a vacation like they buy a giant screen TV before the Super Bowl, with the intention of cancelling/returning it later. You usually need to bail because something big came up that you couldn't possibly have planned for. But what if need to cancel your cruise. Easy peasy, right?
LOL. And you thought the airlines were bad.
Unlike said airlines that simply slap you with a $150-$200 penalty to change or cancel your flight, unless you cancel a cruise more than 91 days in advance, you are going to eat the cost. And you're not just going to eat the cost of the cruise itself; you're eating the cost of any hotels and excursions booked as part of your package, possibly the fees charged for canceling, and, let's not forget, the airfare you likely booked separately.
It might sting to pay the extra money for travel insurance after shelling out all that cash on the cruise itself, but would you rather pony up 4-9% of the total trip cost now or potentially be out 100% of thousands in the future?