Far from being overwhelmed by your post, I rather enjoyed the guided tour. My guess is the death penalty, which came to be attached to the commandment, drove the developments you outlined. Once again, the rabbis appear to have sought ways to reduce the chance the penalty might actually be applied. If so, I stand with them.
As you note, Jesus expanded the commandment's range to include all women. Later, though precisely when is hard to say, Christians took the matter one step farther by making the commandment's prohibition apply to women as well as men.
When I reflect on the Seventh Commandment, several things come to mind.
First, it was and is intended to protect community. Trust of any kind between adults is impossible, if one must always be on watch to make sure no one "steals" one's spouse!
Second, the commandment challenges our biology. For better or worse, we appear to be a species that values monogomy yet finds its consistent practice very difficult. Chalk it up to our fallenness or to evolution--either way, many humans have a wandering eye through much of life. Jesus ups the stakes considerably, when he insists that internal lust amounts to adultery as surely as the act itself.
We may react in at least two ways. A fair percentage of us ignore the commandment as unrealistic. The argument goes something like this: We have a biological drive to have multiple sexual partners over the course of a lifetime; therefore, we have little choice but to do so. In fact "the rules" (whether the commandment or some other stricture) ought to give way to our need. In my pastoral experience, those who take this course generally leave disaster in their wake.
At the opposite extreme are those who seek to honor the commandment by denying the essential goodness of the human sexual drive. Their line of reasoning might be described as follows: God has forbidden one way of satisfying our sexual impulse, therefore, the impulse itself must be a sin; sex must be restricted to procreation and the sexual impulse guarded against at all other times.
Neither approach takes God, community or the human condition seriously. Healthy boundaries are neccesary if one is to manage one's humanity, take part in developing community or learn to live in harmony with God. The Seventh Commandment is one such boundary condition.
Third, by implication the commandment places quite a burden on married persons. If a marriage is to be immunized against adultery, both partners must work at building a relationship deep and satisfying enough to bind themselves to one another. Listening, courtesy, kindness, giving one another room while never losing touch, shared tasks, clearing hurdles together, the worship of God and the like tend to build such a bond, given time. Surely somone who had never heard the commandment might react by saying, "Marriage may be the greatest relational challenge two humans can face."
Fourth, Christians have long associated fidelity in marriage and fidelity to God. Blame it on Hosea, if you will. The Christian point is that marriage (along with parenthood) provides an excellent, comprehensible way to begin to fathom the dynamics of the God/human relationship.
Finally, and by the way, the commandment implies strongly that we cannot easily separate individual morality (for lack of a better term) from matters of the family and the larger community. That's probably a rabbit we need not chase, but I could resist mentioning it!