Read your policy and become familiar with the loss settlement language. I have USAA and it has "Fair Market Value," which is broader than the common "Actual Cash Value." It allowed me to pull ads within my area (150 mile radius) and show that getting a comparable vehicle would cost a few thousand more than blue book. Also, make an itemized list with receipts of every modification. Service records and photos will help build your case that your car was above and beyond. I don't remember the name of the software off the top of my head, but they probably don't use NADA or KBB. Their software gives the adjuster a price and you need to provide a reason for them to give you more; you're trying to reduce the depreciation because your car was better.
I've worked in insurance for 7 years and dealt with this first hand for myself 2 years ago. My first settlement offer was 8500 and I ended up with 11500.
Good Luck OP!
2007 SGM E90 335i
JB4 G4, Mr.5 Intake, VRSF 7" FMIC, ER Sport Oil Cooler, RB PCV Valve, Cyba Scoops and Quad Tips, 17x9 ET30 and 17x9.5 ET35 Concave Apex Arc 8