I've had some of the same thoughts about my own card game. Here's one adjustment you could make to your option 1: if one player has purchased the additional units (cards), then both players get to use them. This is what Blizzard has just enabled for Starcraft II, and is what Goko (sigh) did for Dominion. (please do not use Goko as a model overall however - I can't stand the UX)