Wow, you're not short on info in this thread.
I'm no expert, but I'll try to give my thoughts on a couple of your points:
Water-vs apple juice in the pan. Water is all you need. It essentially is just a big damper for the heat, nothing more. The water will evaporate and it will raise the humidity in your smoker, but this will have more of an effect on the outside texture and appearance of your food, not the internal moisture. Try a couple things, first, pour a quart of apple juice in a skillet. Then crank the heat to high. Let it sit there and boil for 20 minutes or so. Then, look at what you have in the pan. It's concentrated apple juice. The water boiled off, the apple juice didn't. Don't believe me, add water to bring it back to the original quantity. You now have reconstituted apple juice. It'll taste different because it's been cooked, but it's got all the same amount of sugar and appley stuff it did to begin with. My point being, the only things that will evaporate and end up in the steam are water and alcohol. All the flavor components stay in the pan and concentrate, potentially leaving you with a sugary, syrupy sludge that will be a pain to clean. As for steam making your food moist, try steaming a chicken breast. It'll be dry as a bone. The only way the steam will get INTO your food, is if it's under pressure.
On your tough ribs, the no pullback comment makes me think you may have undercooked them as well. Were they dry? If they were moist and tough, they were undercooked. Dry and tough, overcooked. Depending on how you like them, an hour or so tightly wrapped in foil with a couple tablespoons of liquid will help break down connective tissue and tenderize your meat. In this case, the liquid is in contact with the meat, and can be reserved to make a glaze, so flavor is important. Apple juice, cider vinegar, wine, beer, pickle juice etc... all can add flavor/moisture. You've essentially created a mini pressure steamer by wrapping the foil tightly, and you're braising the meat.
Good luck and let us know what happens next time!!