Odd dent, but it doesn't look too bad. Devalue loss is hard to calculate, but if you had planned a total restore, it might add a hundred or 2 to that price. If total restore is well into the future, I would clean up the rust, carefully fill with epoxy, carefully touchup the paint (blend some Testors to get it just right) and then cover it with a clamp. The key would be to fix just the immediate area of the hole without affecting anything else. This way you stabilize and hide the dent, and then defer the real fix to the future.

Bummer on the dent, though. I bought a bike recently that had a decent size dent under a clamp. I was rather perturbed. I was fairly successful in rolling out the dent; however now I need to paint, which I really did not plan to do.

Good Luck

-Gary