I had a similar experence. My '86 truck was hit by a pizza delivery guy in a GMC Jimmy. He clipped my driver side rear and flipped/slid 450 ft down the road. Hit an Explorer behind me as well. Adjuster came out and said damages would cost $1500-$2000 to fix. Got a check from Safe Auto the next week for $796. I got estimates for $2000 then spent the better part of the next year getting them to pay me the $2000.

They said:
"your trucks not worth the $796"

I have a $4000 LCE stroker motor with 25k miles on it, $500 in PRP bucket seats, $1000 rear disk brake upgrade, all of which I offered to provide documentation of.

Next they say:
"If we give you more money we will have to total your vehicle and come pick it up for salvage"

To which I replied " can't let you do that !"
I then filed a complaint with the Louisiana Insurance Commission. I was asked on the complaint form what I considered a satisfactory resolution. I wrote a " a check for the $2000 of damage and no listing of my truck as totaled" Now instead of calling four times a day and getting the claims supervisors voice mail and never a reply, they are calling me.

Now it's
"$2500 and we come get your truck"

My reply " I hate repeating myself " can't let you do that" "

Adjuster says "guess you will have to litigate it"

My reply " thanks for the advice", click.

Two hours later I get the call "My Manager has authorized me to pay you the $2000 if you sign the release of future claim form"

A couple of faxes and a few days later and I have my damages in hand.

They tried every trick known, "Bring it to a shop and file a supplemental claim" , etc. to not pay me any more.
Basically if it's yours and they damage it they have to pay you the cost of the damages. Laws differ by state but if you stick to your guns they have to pay.
Your best option is to get a comprehensive policy for the apraised value of your vehicle. Then when you're hit your insurance will pay you and then go after the other company