In the insurance company's defense (can't believe I just said that) they have set your annual rates based on the bluebook value of your car. Because you do not have an appraised value policy on your car, they've based this on the NADA, etc values. It's understandable that that is all they'd be willing to shell out in case of a claim because that's all the insurance you paid for.
This very reason is why I am switching over to collector car insurance shortly with an appraised value. My Z is no show car, but it definitely is worth more then the average bluebook value.
Best of luck with your claim, hopefully your persistenace will win out!!
BTW, I pay close to $3300 / year for my 18 year old son's 2001 Jetta turbo, which to me is insane. In two year's time I will have paid them the entire value of the car!! He's carried on my policy with no traffic violations or accidents. As a matter of fact, the entire family, 4 drivers, 4 cars do not have tickets and we have never filed a claim!!