I was once informed that my cargo, (B747F), was more valuable than the aircraft and crew put together! We were carrying the major part of an art exhibition that was going overseas for a while. It would be a rather stupid act to deliberately under declare the value of a cargo in the hope of reducing costs. The cargo will be covered up to normal policy limits for cargo, as stated, by the carrier, but the owners would be expected to arrange any additional cover that was required.