Your own car insurance should cover you for a rental worth up to the same value as what you insure at home... with the same deductable and risk of increase to your premiums if you make a claim. Plus, if you are in an accident, or worse on return of the car the rental has damage, you will be in for some hours of contacting your insurance, paying the deductable, and getting the rental company to NOT charge you for the full damage amount while waiting for their check from the insurance company. Plus, the rental company starts with an inflated loss claim that includes loss of use and an inflated value for a car that is certainly paid for many times over from rental income.
That said, I usually decline it too and take my changes and drive carefully and park out of the way. You should carry your insurance card and declarations page to help but I usually forget to do that.
When I rent a car outside the US I always take the insurances. Don't add another country's legal system to the risk!