The original bump deal was for vouchers and BE seating. There definitely is some value to that, so you can make a claim that you deserve some compensation for it being unavailable. (Regardless of how you got it, you got it. If you were flying on award tickets or vouchers (out of pocket cost = $0), and you got bumped from that flight, you'd be just as eligible for compensation as someone who paid for their ticket). As other suggested, you'd probably get another Delta voucher, perhaps Skymiles if you asked for them).
If you'd prefer the voucher, I'd do some additional asking to find out if it is combineable with the ones you already received. I think some are not combineable (and/or their is a limit to how many you can use for one purchase). If DL was to give you additional $$, I'm not sure if they can cancel your existing ones, and issue one new one for the new total, otherwise you might have to book two or more separate trips with Delta.
No one ever likes to be involuntarily bumped or downgraded, but there is an order of who they pull full. It doesn't surprise me that a passenger with no DL status, who was upgraded to first, would be one of the first people to be downgraded. That's travel.
Jeff