I've usually dropped collision coverage on cars when they get under around $15K. (All but one of my cars was purchased for less than this, often much less.)

If I had a 0% loan on it for some reason at that point, that meant paying off the loan to let me do that. (If you assume an 8% nominal return on investments, that means when paying off the loan would cost me under $100/mo.)

I think you should insure against risks that would be a substantial impact to your life and (generally) not insure against risks that wouldn't.