Diminished value
"In the past decade, a number of courts have squarely addressed the issue of diminished value claims under comprehensive and collision auto insurance coverages."
The majority of these courts have ruled that comprehensive and collision coverage limit liability to payments for proper repairs and do not provide for payments for losses in value, he says. State supreme courts that have set this precedent include those in Delaware, Indiana, Florida, Maine, Massachusetts, South Carolina, South Dakota and Texas. A few appellate courts have made similar rulings, including those in Illinois, Louisiana, Missouri, Pennsylvania, Tennessee and Wisconsin.
One of the reasons courts are ruling as noted above is that it's difficult to determine the diminished value of a car immediately after an accident. The car is not being sold at that moment. If it was, then one could fairly easily calculate the difference in price between an undamaged car of similar age and condition to the damaged car. You would then be claiming an actual loss rather than a potential loss of value.
However, what if the owner of that now damaged car will keep it for 2 more years, 5 more years, etc.? How can someone accurately determine the diminished value that far down the road? If one plans to keep the car, it is repaired to spec and handles as it did before, then there is, perhaps arguably, no difference in economic value.
Now, I understand the anger and frustration of being hit by a nimrod in some POS who chooses to avoid checking his rear view mirror or is texting while driving. I've had each of those happen to me (the first situation twice) and I was pissed.
Good luck to the OP on the repairs. Make sure you thoroughly shake down your car after the repair and check things like uniformity of spacing where the quarter panels, doors and bumper meet. Auto repair is so much better now than back in the day, but even the best shops may occasionally get sloppy. If you haven't done so already, check around to see what body shops in your area really know how to repair BMWs. They will do a better job and find a lot of little things that other shops may miss. Push back at the insurer of the other car, or your insurer depending on how your claim is being handled, if they try to direct you to a shop that isn't to your liking.