There are one thousand "blurbs" given to a traveler during a trip that summarize complex rules. Think "3-1-1." One more couldn't kill them.
Seems that some English major could come up with something to say during VDB that would keep customers from being P.O.ed. Maybe as simple as
If you would like to take the next flight, we will offer you 400 Delta dollars. These are only good for you or a companion, and cannot be used with another voucher.
I would think that would cover 99% of the upset VDBers.