Steve Landsburg makes a fairly plausible case that monogamy is essentially a cartel formed by men to prevent them having to work too hard to keep onto their wives:

imagine a one-husband one-wife family where an argument has begun over whose turn it is to do the dishes. If polygamy were legal, the wife could threaten to leave and go marry the couple next door unless the husband conceded that it is his turn. With polygamy outlawed, she does not have this option and might end up with dishpan hands.

If true, this would suggest that women have more to gain from polyamory than men on average (although high-status men might well have the most to gain).