For higher base rarity cards could add some soulforge items to their disenchantment such as colored gems and diamonds.
Mythics: 20 of each color gem they represent and 5 diamonds
Legendary: 10 of the color gem they represent
Epic: 1 of each color they represent
UR: 25 shards
Rare: 10 shards
common: 1 shard
This would make getting gems a little less grindy and it would also give a useful place for the excess troops to go.