I may be mistaken but can you even buy BOFFs with dilithium? I thought the BOFF vendor on ESD/Qo'nos only sold white quality BOFFs for EC? In which case, why do BOFFs have a stated dilithium value at all?
To the OP: yes you don't get squat for dismissing a BOFF. Your best hope is to get some EC out of him on the exchange. To be "fair" it's always been like this, even before dilithium.
Yes you can buy BOFF candidates on ESD for dilithium. You still train them with BOFF skill points (I think that's what they're called.) Based on that, IMHO, it is reasonable to believe that you could sell them for dilithium. But, you can't.