The summer before last my 2008 Winnebago Vista was struck by a vehicle while parked in front of my residence. There was $12,500 damage done to the motor home. After the Winnebago was repaired I had a professional appraisal done and sent a demand letter for compensation, for diminished value, to the drivers insurance company. I had sought advice from my attorney who advised that the amount of damages weren't sufficient to warrant paying him to handle it for me.
The process was not fun and entailed a number of back and forth communications with the insurance over a period of 9 months. They tried to settle with me quickly for an amount much less than the real damages but I stuck to my guns and was adamant that I would be "made whole". In the end I received compensation for not only diminished value but "loss of use" as well. The amount of the settlement wasn't the amount I originally requested but MUCH more than their original offer and definitely enough to make the "battle" and time investment worthwhile.
As I learned, the diminished value laws vary by state and many states do not allow claims for diminished value against your own insurance company.