Don't necessarily get replacement value for the aircraft you rent.
Like all decisions like this, this is a business decision on your
part. On one side the risk of lossing an asset, on the other the price
of the policy. In the 25 years my broker has been selling insurance no
insurance company has sued a pilot on any of his FBO policies. Decide
for yourself, but if it were me, I'd only get enough to cover the FBOs
deductable and loss of use. Remember that lawyers cost money, suing
cost money, and insurance companies are working hard not to spend
money.