Redesign upgraded cards' art. Entrants pick one upgraded card that has the same art as it's unupgraded version and give it new art.
You could either do this for every card in the game, or per element. Personally, I'd say per element otherwise you might not get many repeated cards and it'll be hard to compare which is the best as they'd all be for different cards. Pillars not included because they just got new artwork.