Take the car to a reputable mercedes mechanic or restorer and get an estimate on what it would take to make your car the way it was before the accident. My sister (not a benz owner) was hit by a taxi and the insurance co gave her $2000 - what they thought was the total value of the car (generous by my extimates) My dad took her car to a repair shop and they fixed it for $200. Please not there was no frame damage. My sister walked away with her car in the same shape or better than before and with $1800 to put towards her tuition that year. You're right in that you probably won't find a comparable value with what they give you, but if you're car is in as good a shape as you think it is you should be able to fix it. See what a technician has to say, but be prepared to bite the bullet it the damage is more extensive than you thought it was. You don't want to have your wife driving a car that's not as safe as it used to be for just for sentimental reasons. I do know that in a lot of cases, insurers write of cars that are perfectly fixable.
PS Make sure you go to a reputable shop. There are some people who will take your money and tell you they can make your car whole again even if they know it will not stand up to another accident.