One of the ways I have thought of a card system working was a bit more tactical.
During your attack phase each player is dealt one card per model/unit's attack. They can now place them, face down, next to the model that will be making their attack. The number on the card is the attack value + skills + modifiers. Either take out the face cards or make them something special like critical hit/miss, weapon jam/break, etc. This way you can see what values you will get at the beginning of the round and will be able to balance where your bad luck (low cards) go.
Just another off the wall shot.