Diminished Value Claim (CA) for minor damage in 4-car Pile-Up?

[afadeev]

DV for repainting a plastic bumper cover? Will that even show up in the vehicle's history?

DV is not for the magnitude of the repairs, but for the mere fact that a used car buyer will raise red flags over the fact that there was an accident, and that it may not have been repaired fully or properly.
Used cars with accident history always cost less than clean used cars.

Just for reference - BMW commonly resprays front and rear bumpers on CPO cars before putting them up for sale.

That is completely FALSE.
Bumper respray will cost you $600-850, and no-one will eat that cost "commonly".