Not so much a content idea, but ...

[Super Buu]

Aye, I was thinking about the same thing. But it would get pretty difficult for the staff to judge. I think with this, the member can get a good idea of the reward they're shooting for beforehand, and the maximum adjustment is only half or double. So the staff don't just have to pull some numbers out of nowhere. Basically keeping the quest system as it is, but adding some flexibility.

Edit: This would also negate the clumsy necessity of asking a member to write more if they haven't met the requirements - instead, just give them a penalty