Wow this is the first I've ever heard of "diminished value claims". Makes perfect sense to me though.
Wish I'd have know about this 3 years ago when my (then new) truck was hit by someone. It was side-swiped, taking out the fender, hood and both drivers-side doors. Though the damage was all really cosmetic all panels were replaced, so I'm sure on a Car-Fax or whatever it probably looks like there was a large amount of damage. IIRC it was like $6-8k in repairs.
So from a buyers perspective I'm sure it probably looks like the truck received significant damages.
I thought right then that it would probably have a drastic effect on the truck's value. Wouldl have definitely filed a diminished claim if I'd known of such a thing...