You're right.

My gut inclination is to to say "there are lots of impacts that we can't quantify, but there would also have been lots of impacts that we couldn't quantify in the case of the counterfactual, and I don't imagine that they would have been systematically better in one case or the other, so I'll ignore such impacts" but this feels like a dodge. Do you have any thoughts there?

I do think that the "how much would people have been willing to pay for it?" metric picks up on more qualitative impacts than might initially meet the eye.