I'm going through the same thing right now - I bought a beautiful low mileage '10 335i X-drive M-Sport in March got hit in August, got the car back in September and got hit even bigger in October. Neither accident was my fault so I am pursuing diminished value claims in both cases.
Assuming I get made basically whole I will then dump the '10 for a ED F30.
I don't want to recommend the company I'm working with because I have not had success yet with the DV claims but if I'm ultimately successful I will let you all know.
Do your research seems like a legitimate way to get made whole. However, to earlier points it also proves that Insurance companies are profit centers and not out for their customers. Because if they were they would pay out the DV on your vehicle automatically instead of spawning a whole industry to deal with DV claims.
Insurance companies of course claim that if they automatically pay DV claims that rates would go up across the board to cover the additional expenses. So if the customer doesn't bring it up they will not pay out period.