I think this is a case of discussing apples & oranges... First there's flexible flight - I believe all major US airlines offer the option of changing flights before first departure, & there are no longer any cancellation fees for flights. So if you book with a US carrier (and not a discount airline) & are willing to travel within 12 months, you don't need to pay up for flexible flights. The $$ goes back into your account to be used on any flight within 12 months.
Second there's travel insurance - I'm just not going to skip having trip interruption & medical evacuation insurance! Check the credit card you're using for flights, that may well have (some) travel interruption insurance. I don't consider what's offered by the airline when you book flights to be enough insurance.
I pay $265 per year(in my late 60's) for "GeoBlue Trekker Choice" insurance, good for multiple trips per year. There are lots of others people on the Forum recommend highly.
PS, There are many reasons you might need trip interruption insurance, many people have written about their experiences getting stuck somewhere without travel interruption & evacuation insurance. BTW, Overseas Adventure Travel requires you to carry this kind of insurance, because DUH, stuff happens! (Israel a month ago?!)