I have one bicycle that has a small wrinkle in a tube, my Zullo.
Sizable enough that I am keeping her around for light Sunday rides, but certainly not offering her for resale.
I keep her because she is a pretty frameset, and i love to look at her!
As for buying something with a ding/dent, I usually wouldn't give a bicycle frame a second look with this defect.
However, I have a friend that raced an Independent Fabrications cyclocross bicycle this last fall.
It has a decent handlebar ding in the tt, and he's offering it to me for peanuts.
I need a racing frameset for the Almonzo 100 in the spring, and this may be the right one.
So, I won't be buying this for looks, and it will probably be safe enough.
I'm still going to have a local builder look at it to give it a diagnosis before I buy it.