Why is the ticket value even taken into consideration? They're still flying you where you need to go, so you're using that ticket. What they did to you was delay you.

It would follow that the only thing that really should be factored is impact to one's schedule, and compensation should be a function of that impact.

Paying someone $350 for an OAK-LAX bump when the next flight is in an hour is a bit excessive.

Similarly, paying someone $299 for BWI-SEA when the next flight with space is in 8 hours is probably on the cheap side.

Any time an airline has fixed costs for VDBs, it impacts the ability of the GA to get the right volunteers. In the OAK-LAX example, someone's getting a sweet deal. In BWI-SEA, it might be tough to get people.