I have the AMEX premium insurance which offers significant increases in coverage.
It is a one time fee for each rental up to a maximum number of days, I think 40 something,
for $29. I spent a considerable amount of time talking to them about this and they advised
taking only the basic insurance. You have to sign the waiver of $1200 for damage with the
rental company but Amex says that they refund it and work out the details of damage with the
vendor. Fortunately, haven't had to find out how it works but AMEX has been great in the past
resolving disputes for me.