Randy, just looked at mine and that missing section shouldn't affect anything. That little "boxed" area immediately to the right of the void is how the hood secures to the lens. The missing piece is an empty space and how the notches on the hood clear the notches on the lens to mount and reverse the hood.
As for value, I would venture a guess that it would take off $50-75 since the hood
should still be fully functional
Edit: My guess is it could be fixed, but I can't see it coming in at under $200