Well, I think (personally) that Stardock should add *legal* polygamy as an advantage, and faithful monagamy as a "disadvantage"**
**its not actually a disadvantage, but by maintaning Morale Authority, you are able to spend more points on other facets of life, its not to say that monogamy is "worse" merely that it allows you to be a better person in other areas. Likely Faithful Monagamists and Legal Polygamists would be at opposing ends, and thus have diplomatic difficulties.
So ... the DEFAULT would simply be legal monogamy, with a chance to sire bastard children as well.
This seem like the most logical consideration. Bastard children *could* give you extra champions, but they could also get mad at you and stir up revolt. Do you decide to barr of bastard children fofr good? or do you spend points to have multiple queens (as opposed to mistresses) in order to keep all your Children loyal?
-I suppose there could be a similar option for Female Sovereigns, although im not exactly sure what the benefits/penalties could be ... as you can't exactly have *more* children through infidelity as a female ... unless being so merely means an increased chance of fertility, as the female's eggs are being fertilized by many consorts there is a greater chance that a successful Zygote will be formed. The downside would be that your illigitamit offspring would also be "bastards" (I think?) ... or maybe since the Sov is the mother, there would be no bastards, but maybe you would lose your Spouse every time you sired a bastard, thus (at least temporarily) decreasing your chances of having another child. However, if you legalize Polygamy, you could have many pleased Kings and thus maximize your chances of getting pregnant (based upon the fertility of your spouses).
Of course, the numbers of Children between faithful and legalized faithlessness are much greater for Males, so probably a greater point-spread for Males. (because a faithful Male and faithful Female would have the same approximate number of children, but an unfaithful male would have MANY more children than an unfaithful Female ... on Average). And that average quickly turns into *every game* when it spans many generations of spouses.
Another "advantage" of legal polygamy is that there is a much greater chance (almost 100%) that there will be at least 1 living spouse at any given time, since if your "harem" of 3-5 decreases by one due to a Death, you can always marry another to "replenish the ranks."
Another "disadvantage" of the Male being faithfully Monagamous is the amount of time NO children can be born between the time when their Wife grows infertile to the time when she dies. As there are no mistresses or other wives to fill in the gap. Thus being a Faithful Husband gives MORE points back to spend than being a faithful Wife. Also, being an Unfaithful Husband COSTS more points than being an Unfaithful Wife.