I agree that God as the agent of ultimate redemption is stupid and leads of course to simple power problems. Humans can pretend to wield part of that great power, e.g. confession in Catholicism, and that power gets abused in one way or another.
I wouldn't hesitate any moment to claim that overall you find more crap than useful stuff in religious texts. But then again I also think that the nasty stuff in them as well as organized religion is obvious so it is more interesting to find the not-so-bad and not-so-obvious ideas.
Let's stay e.g with tge "Christ died for our sins" notion. It also has some nice implications that do not involve any metaphysical power figure. It does after all not mean that we messed up, now the slate is clean and now we can mess up again. It rather means, time-travel paradox style, that this act created the very possibility of redemption. This can make people more forgiving and my personal experiences with Christian is that this is indeed the case (but then again my personal experiences are hardly representative as I do not personally know any Christian right-wingers who obviously prefer revenge to forgiveness).
About the point of monotheistic religions, of course they are as you rightly pointed out a way to structure society and wield power. But I also think that they are a progress from pagan religions where gods stood for natural processes which have not been understood yet. Yahwe on the other hand stands for the law, for abstract stuff (hence the forbidding of making a picture of God in Judaism) which is some kind of progress. And in the Jesus story God even dies so it is a stepping stone towards atheism, more progress.
I admit that my reading of the text is basically a left-wing one, Jesus wants to create a community of equals beyond tribal bounds (if anyone comes to me and does not hate father and mother, wife and children, brothers and sisters, yes, even their own life, such a person cannot be my disciple) and his notion of God equals this very community (for where two or three gather in my name, there am I with them) so when Jesus the man dies all that is left is this emancipatory group.
I don't think that this reading is entirely correct but I also think that it is a closer and more truthful reading than the Christian orthodox or fundamentalist interpretation. Or wouldn't you say that a Martin Luther King or Oscar Romero have more to do with the Jesus story than a stupid Pope?
Of course I gotta admit my motivation is also partly strategical, bashing a right-winger with his own holy book is potentially more powerful (and fun) than bashing him with secularism.