I insure what I cannot afford to lose.
Generally, with a land-based trip, there is not a lot in "non-refundable" costs if you have to cancel. I think with Disney, if you cancel a package, the most you can lose is $200. For my family we usually drive, so there's no airfare to be concerned with. I'm not going to spend $120-150 to insure $200. That doesn't make sense, since the most I'd get back is really about $80 (the $200 non-refundable costs less the insurance premium, which is never refundable).
Medical costs are generally not a concern on a land-based trip because my personal health insurance is good anywhere in the country for emergent care provided out-of-network...but my in-network coverage is pretty broad so I can always find a doctor/hospital where only my co-pay would be required.
But we also cruise as a family...and those costs are more "sunk", meaning non-refundable. Final payments are due up to 100 days prior, and significant cancellation penalties exist. At a week or two out, if something happens and we have to cancel, we could suffer a loss in the thousands of dollars. If a medical emergency occurs at sea, my own health insurance will only cover life-threatening emergencies, and won't pay for a medical evacuation. Those are some big-ticket expenses that can cripple a person's budget. In those cases, I'll ALWAYS spend the extra $$ for insurance. Its peace-of-mind, and well-worth it.