If you insist, it's hard work, but the insurers have to make sure you are in the same situation as pre-accident. Therefore you can insist that the car is repaired as long as there are no safety implications to the repair.
Also get copies of any adverts of similar cars from all over the country so that if they make you a low offer you have evidence to show that you can replace your car for the monies they have offered.
Sorry it had to happen to you and to a Lexus, what with all the other cars out there it could have been