There is strong dissension amongst the brethren over the prospect of polygyny.
What I find fascinating is how strong the opposition is to any concept of concubinage. The pressure bury it in the OT is, to me, an indication that the enemy fears this as s useful tool also.
Steve, I am not specifically speaking to you, I am just mentioning things that came to my mind after having read your post.
I think one of the routes by which this has been accomplished is with a grand misinformation campaign. I have read a number of Christian writers who seem to perceive concubine as the dictionary term for sex-slave. Then they proceed to effort to explain why God "allowed" such "evil" things in the "Old Testament". I expect that for many of them, the man who has more than one wife is little if at all better (in their eyes) than the man who has a concubine ("sex-slave"). I've read many comments (youtube, blogs, articles) from women who seem fully persuaded (and even angry perhaps) that polygyny has no benefits for women what so ever, but only for the man, and that is; sex.
I think that defending polygyny and concubinage might benefit from a tac of separating exactly what is being defended from what is not. Many seem to approach poly in the bible as if they already know it's wrong, and then dig up whatever they can to "prove" it. Arguing scripture with these might not be as effective as determining why they already "know" that poly is wrong, and then showing them the facts of how their understanding is wrong. I think that those "facts" which were used to conclude that poly is wrong might be a significantly more assailable target than the outgrowths of that, which is their "knowledge" that poly is wrong and the bible verses they use to "prove" it.
I am pretty sure that I have seen people arguing where both are right in their own position but misunderstood each other's position, and therefore thought the other was wrong. I am almost certain that I have been of them even recently. Had they discovered that they misunderstood each other's position, they might have discovered a great deal of common ground on the topic they thought each other was so wrong about. Reasonable people, each having quality information, seem to oft arrive at the same conclusion. I see a lot of what appears to be deliberate corruption of information including meanings of words, and misframing of the situation. That misframing is misinformation about the frame of the debate, which is put forth as a self evident fact that is not in dispute. Other things are then put forth as the disputed information. They then proceed to argue within that wrong reference-frame, and this causes one side of the dispute to seem like the obvious winner.
I have tried to reason with people about polygyny and other matters, and it can take repeated and detailed explications of how a certain two things are not synonymous before the frame of the debate can be switched, and the person understand what exactly I am defending, and what I am not. If they think I am defending something that is actually wrong, because right and wrong have been conflated; it seems a battle already lost. Rather, I think that the first step is to strictly define what it is that is being defended, before efforting to defend it. The terms must be properly defined so both sides are thinking the same thing when a certain word is used. Sadly, the person might even think it strange, and that you're mincing words, when you effort to be so specific, when the umbrella term seems just fine. It might even seem that you're trying to generate a distinction where there is none.
I am not of the mind that everyone is even able to hear the truth. I believe that for some, their mental framework for processing information and understanding the world around them is so broken and corrupt, that no amount of truth, in the near term, shall be persuasive. These might have a beloved lie that they want to be true (feminists?), and so whatever comes along that might conflict with that lie is not soon accepted. Some might even shutdown as they see truths arrive, which they cannot dispute, that are chipping away at the foundation of their beloved lie.
As for concubinage being a useful tool; I think that we see all kinds of problems caused (at least in the sense of being a link in the causal chain) by large numbers of women going around who are not ruled over by a man. The process of easy divorce, seems like more of the same; resulting in mass numbers of woman not being ruled over by a man.