I'm in the Spencer camp on this, not villainy, but bleh ...
Of course cards, due to the need for uncertainty in the opposing player's mind, would not suit solo play, my main mode.
The plus for cards is that they introduce extra fog of war and uncertainty. The negative is that if not limited in scope then card play may have the effect either or both of skewing the balance and taking over the player's attention. I don't want ASL to become a Card Driven Game.
Cards are one way, drawing chits from a common pool, say the player whose player turn it is gets to draw a chit just before his/her player turn. That chit can be used any time after drawing and then discarded. To avoid buggering up balance keep the meanings weak, like a 2nd line HS or a ±1 DRM to any single dr/DR or a wire counter, etc.
Eg. The ±1 DRM could be applied as a -1 to the player's dr/DR or as a +1 to his/her opponent's dr/DR, whatever the first player wants. Keeping the effects weak means there is extra FoW without either upsetting the balance and avoids card/chit play dominating the players thinking.