They owe you the actual cash value of the car. For a normal 2002 Altima calculating that amount is pretty straightforward. It gets more complicated when you have a vehicle that has collector value over and above the vehicle's listed value in such publications such as KBB or NADA. I did a quick check with KBB and the figure you were offered is consistent with their valuation of it. The best advice you have received here is to obtain a professional appraisal to help you prove your Z's actual value exceeds the listed amounts. I would get this before you even contact an attorney and I am one. You might not be able to recover everything you have in your Z, it is possible to over-improve an asset, but I believe it's worth far more than what they have offered you.
GatorJ 1996 300ZX NA 1970 Fairlady Z 1983 280ZX Turbo 2006 Ford Escape Hybrid 4WD