Justin, with your card play idea the attacker has a chance of 1 in 3 to hit the defender. You could just as well roll a dice and hit when the attacker rolls 5 or 6.
I don't think it's a bad start. I think you need to give the defender a motivation to play a particulat card over another, so that the attacker can try to guess which one the defender will play. For example, if the defender plays "duck to the left" he gets closer to the treasure (which is good for him), if he plays "duck to the right" he might fall into the snake pit (which would be bad). Now, it's still a guessing game, but the attacker has some basis on which to make a guess.
Another way to modify that card based system would be to add some type of limiting factor to the 'fancier' cards for the defender... You could have the "Sway to the Left/Right" cards take more energy out of a reserve than the "Stay in the Middle", since dodging is more strenuous than staying still. This could also be reasonably reproduced by just having fewer of the dodges available per battle (Something like 15 "Middles", and 7 each of "Left" and "Right")... Then it can be assumed that the defender will stay still more often than not, giving the attacker some idea of which way to shoot, while still leaving enough options for the defender to avoid the damage.
Another variation on this could be to have different consequences based on the card matchups... If the attacker and defender play the same card (both to the Right, for example), the defender takes full damage, while if they are one step away (Middle vs Left), the defender would take either half or no damage. Then, if the cards are complete opposites (Left vs Right), the defender expertly avoided the attack and is entitled to a free counterattack.
Just a few thoughts on that card based idea...