The most sage advice I've ever been given about insurance is, never insure anything you can afford to lose. This is because the premiums are always set at a level so that, on average, the insurer wins and the customer loses.
For example, I will never insure my mobile phone, because if it was destroyed, it would be annoying, but I could just buy a new one without it really impacting my life. The same logic applies to insuring your insurance. If you had a crash without protecting your NCD, it would be a bummer, but it wouldn't be a financially devastating event. Therefore, you're better off leaving it unprotected.