User blog comment:B214/Question and Answers/@comment-5185939-20131008060026/@comment-5185939-20131008070517

Well, Gift can seemingly increase 'qualities' of items he uses it on. Such as Sirzechs' suggestion to use it on Rias's breasts, or increasing the intensity of his dragon fire.

If that's the case, than theoretically, it could work on the value of an Evil Piece.

I agree it won't happen, but it's an interesting thought.