Lets make this simple.
#1 if it is water damaged walk away unless it is a 1 of one or worth a million dollars where restoration is still under the value. Or sentimental value is greater than the cost of the restoration.
#2 as for bumps dings and bruises that is no different than any other car. Many of todays cars were total rust buckets and in comes to the point they may contain little of the original car after restorations. Know the work done and how extensive before you buy anything.
I saw a 455 SD TA that the drive line some trim and the Vin were all that survived the rust. It was a clean car and it was not storm damaged. But then again the debate and value are based on just how much is this really a 74 455 SD TA at this point. It depends on the buyer if they are aware of the work.
Well documented histories of cars via photos and receipts are key in value. If a seller has little to show then be wary.
As for new cars unless it is high dollar and one of 499 made like an Enzo leave it alone. They did repair the Enzo that crashed and broke in half. Also the Bugatti that crashed in the water was restored if I recall but for their value they could be rebuilt and resold.
Water damage is not for the weak and under funded.
Most cars are not so rare you need to go to heroic measure to save them. Best to find the lowest mile or best documented car you can fine and go with it.