i think it should be possible (maybe also for 1.5k electrum) to downgrade cards, like nymphs. air nymph, for example, could be good in unupgraded and in upgraded decks, but the 3 att.power you get more upgraded are great, still you shouldnt upgrade nymph cause you have a usage in an unupgraded deck too. with "downgrade" option (or card-reset option) you can do both and dont need double amount of nymphs (also gravity nymph from 3 to 4 defense is a great improvement for example.