From memory when I was in the insurance game.

The main reason they don't like Q's is because, they either have a dodgy past and most likely have been paid out on (i.e stolen recovered but with no id or with alot of untraceable parts). Or because they were built from various parts etc, or kitcars.

Basicly in the case of a cossie, they can't prove it was made by ford, and they don't know whats happened to it since it was made, so they are warry of them and charge the friggin earth to cover em.