In Genesis, those who took more than one wife were usually those that did not follow God’s will so well…like the contradiction the line of Cain and the line of Seth.
In Exodus (21:10) God tells Moses that loosely that if a man takes another wife, he must not reduce the amount of food, clothing, or conjugal rights of the first. It is hard to see how a man could treat 700 women equally. Leviticus lays out clearer guidelines about whom a man can marry in terms of blood relations.
The reign of Solomon represents the fall of man from the grace of God in a sense. In the beginning God offered him anything he wanted, and he asked for wisdom, which pleased God and gave him a great beginning in Biblical history. What he did with his wisdom did not always please God. He seemd to be more and more concerned with political ambitions and establishing himself in the world, and less about his relationship with God.
To me, Solomon represents some one more concerned about what his actions signify (look how great he followed the letter of the law), than the substance behind the actions (how poorly he honored the spirit of the law). On the one hand, he built the elaborate first Temple. on the other hand, he had 700 wives.