Should we do a mitzvah out of fear of the consequences if we did not?
Most of this makes sense to me. We are all aware that lying or cheating once is rather hard, but it becomes easier once it's been done and is now in our arsenal of actions. Similarly, a mitzvah can lead to another mitzvah - either by yourself (because it's so rewarding to do something good that you may want to do it again and get that "rush") or by somebody else, along the lines of "pay it forward".
However, doing any mitzvah, a small one as well as a large one, just because you don't know the rewards or punishments associated with each one is quite problematic to me. I believe that we're supposed to do mitzvot for their own sake - because it's what God wants from us - and not with an eye on some future reward. Similarly, desisting from doing evil because of fear of the punishment is not why we are supposed to do the right thing. This carrot/stick paradigm works with young children (mostly), but as we mature, this should not determine how we behave. To take the usual and highly simplistic example, why do you stop at a stop sign at 3 AM? You would see the lights of any other cars that were coming and so wouldn't go if you thought there was a risk of danger. And there's essentially no risk of your getting a ticket at 3 AM. But you stop at the stop sign because an orderly society that follows the rules of the road minimizes accidents (there won't be two people trying to occupy the same intersection at the same time), and we practice this orderliness for that very reason - because we are contributing to overall public safety, not for fear of the consequences.