Like has already been mentioned, it depends on the damage, obviously, but it also depends on the car and your desire to rebuild it. I've rebuilt two '88 Thunderbirds that were hit pretty hard on front ends. Why?
1. Because I was able to get them at a very good price.
2. Because I happen to really like that body-style, and have had a lot of experience with them.
So, it's really up to you. What are your plans for the car? Rebuild it and sell it? Rebuild it and drive it till it drops? Rebuild it as a nice hot-rod project? Those are all things that only you can determine the value of.
The last TBird I picked up and rebuilt was an '88 Sport that suffered an impact of about 30-35 mph from the right front corner. I was able to pick it up from the owner, who included all new sheetmetal, lights, nose, hood, etc. for $1350. The car had <50k miles on the clock when I picked it up. After some hard work and TLC by myself and some good friends (PRICELESS!!), it was on the road and my daily driver for another 100k+ miles. I kept things mostly stock looking, but I was also able to bolt in quite a few go-fast parts after the initial rebuild. I was probably into it for about another $1000 just to get it roadworthy again, but then the mods started, and I spent a lot more for all the goodies. It did (and still does) carry a "branded title ("REBUILT/RESTORED"), but it was my personal favorite of the many Thunderbirds that I've owned and built. In the end, I didn't really get the money out of it that I would have if it didn;t have the branded title, but I got way more personal satisfaction and enjoyment out of it than money could buy.
Here's the end result of my initial $1350 purchase...after 6 years of driving her.