What about a new terrain type, called Treasure that acts just like Victory except it disappears (changes to Open) after being claimed?
Great idea, but I don't think there's any current way to get scripting that spawns/despawns things in the game. However - maybe it could get treated like a creature - and drop off the board somehow when claimed, like it had been killed...
I was talking to @Farbs about something related to this, I don't remember what he said about the feasibility of implementing scripted events that would add or remove attachments but it's definitely of interest to the devs... here's hoping!