Well, I guess "You could do this Night card as a Treasure worth 0$" goes for Changeling, Exorcist, Vampire, Bat, Werewolf and Cobbler, too. Of course a Treasure version also could be worded to keep it from trashing itself. Hum...
I thought about other things it could do. If it always just upgraded itself, it would be too similar to Changeling.
If it converted coins into draw (for next turn), it would be a duration-Storyteller.
If it just gained a card, it would be a nonterminal +buy.
If it just trashes a card from hand, it would be Salvager.
Other things I could do would be having it be a Scheme for several cards, a Scavanger for several cards, or a Remake for several cards. Like:
"Pay any amount of $. Per 1$ you paid, trash a card from your hand and gain a card costing (up to/exactly) 1$ more."