There's no hard-and-fast answer to this. Trip delay insurance is probably most useful if you're a frequent traveler, as there will be more instances in which your trips might be delayed. At the same time, you might find insurance valuable just for peace of mind on an occasional trip.
If you're willing to shop around, there are travel credit cards with annual fees under $100/year that come with trip delay insurance. However, keep in mind that the most comprehensive insurance policies usually come with premium cards that charge higher annual fees.