All of the insurance coverage I have found for instruments used in performance require either "declared value" insurance, for instruments which apprciate in value (collectibles), or insurnace which is set up on a depreciation schedule. "Replacement value" insurance would, for instance, pay only 1/3 of the basis or cost if it were destroyed at the second year of ownership, if the depreciation were figured for "straight line" depreciation over three years.

I have over 300 instruments. Keyboards (except for my B-3's) depreciate like mad.
Collectible guitars, on the other hand, often appreciate in value.

Insuring instruments, especially a LOT of instruments, at a reasonable cost is an expensive, necessary part of the business.
In the last 40 years, I have had instruments crushed, stolen, trashed, etc. I try to play "junkers" instead of collectibles for certain types of jobs.

Russ