So treasure cards are almost exactly like action cards, except you play them during the buy phase. They take up a card slot in your hand, but don't take up an action. So, what if all treasure cards were just regular action cards, and "buy phase" was just the phase when you buy a card, nothing else?
Also, let's say that cards that reference treasure cards (Bank, Loan, Mine, Mint, etc) still work the same... perhaps the new treasure actions have a subtype treasure... this subtype doesn't change anything, but it allows other cards to reference them.
Copper: +1 action, +1 $
Silver: +1 action, +2 $
Gold: +1 action, +3 $
So what would be different? Just a few things off the top of my head:
- Tactician would be way more powerful.
- Terminal card drawers in general would be pretty bad.
- Adventurer would be worse.
- Mandarin would be more powerful... basically all the tricks that you could only do with Black Market can be done always now.
- Conspirator would be brokenly awesome.
- Shanty Town would be worse.
- King's Court and Throne room would be insane.
What else would become great? What else would become crap?