The insurance company doesn't care what kind of condition your car is in, they go by algorithms based on the original sales price of the car, average mileage, average depreciation, and average condition. You're paying the same insurance rate for a showroom-quality example as someone driving around with literal see-through rust holes in the doors.

Unless you have a contractual "agreed value" insurance policy, you're fighting a losing battle. Have a discussion with a nearby wall, you'll get much further with it than you will with the insurance company.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)