I considered only having Perpetuum be triggered by either quanta spent on playing the card (playing a Destroyer would trigger it, but not activating the Destroyer's Growth ability), or quanta spent on abilities (the Growth ability would trigger it, but not the initial summoning of the Destroyer). But only one of the two would, I felt, not be versatile enough for players to use it in their regular decks, leading to what happened to Flooding. I guess the former option could work with Eternity/Perpetuum stalls, but otherwise the card isn't flexible enough for most decks IMO.
EDIT: About the upgraded card's effect, what if I had it generate
instead of
, but still only be triggered by the opponent? That way a clever player could still largely avoid triggering an enemy Perpetuum's effects.