I agree you still have to be careful about the insurance. You said you're concerned about one of your parents taking ill, causing you to cancel. If a parent takes ill due to a pre-existing condition, you still may NOT be covered. There are certain conditions under which you must buy the insurance to also cover someone not traveling with you, and to cover yourselves and immediate family for cancellations due to pre-existing conditions.
Cruise Fanatic also made very good points about the airfare.
Let us know what you decide. At least you know some of the questions to ask.