I always thought that a 75 V8 would be more desireable than the MG ZT 260.
As Cat-D is more of an economical write-off than a technical one, I can't see why it would knock 30% off the price.
A car can be Cat-D because the paint job is a good 3k due to certain colours
From a trader's point of view certainly a bargaining point at P/X but when put on the forecourt for sale all of a sudden Cat-D is 'a minor accident that doesn't even appear on the V5'
Personally I think the car is worth at least 6K, regardless of the insurance marker.