Transmute card to change one type of resource for another at the equivalent tier.
Bank or investment House, when the one time use gold cards can be "invested". Or some other interaction with those gold cards
A card that reduces the cost of the next played card or cards to be free.
A card that increases hand size (perhaps just for this turn)
A card that increases total mana
More effects both positive and negative that have a low chance of happening, perhaps fields could have a bountiful harvest season so 3 turns of double output or something
Some sorta tools upgrade card to get better output or maybe double consume on lumber Mills and/or Masons