Well having an ally in a witch with untapped potential would be useful, but that's not really something to lead with. That's more of a third or fourth conversation kind of topic.

"As I said, I wanted to sate my curiosity." He gestures as if to say 'that's it', even though he's now fully aware Nancy's smart enough to know it's not, "besides, even if I was after something more, I don't know that I've anything worthwhile to offer you in exchange."