I just saw Boniface's post of last May in which he discusses a Monarchial Dilemma. I have only a couple of comments to make in that regard.
1. The first commenter (anonymous) stated that Otto von Habsburg is the last living descendant of Blessed Kaiser Karl I. This is simply not true. Otto is perhaps the last living child of the blessed Kaiser, but he is far from being the last living descendant. In the last count that I saw, he had 7 children, 23 grandchildren, and already 1 great-grandchild. Although Otto is still alive, his eldest son HI&RH Archduke Karl is already the titular Head of the Imperial family.
2. The commenter "Creary" mentioned St. Thomas' De Regno (one should also look at ST I-II 105.1 in which he basically describes constitutional monarchy as the best form of government) in response to Boniface's lament over not having found a good systematic presentation / apologetic for the superiority of monarchy. Unfortunately, I don't know of any modern works along those lines either, but I'll throw out there an even older source instead: St. Thomas draws on Aristotle's Politics; so might we. It should be no surprise, after all, that Aristotle treats this topic a bit more thoroughly than St. Thomas did, since the question of democracy vs. monarchy was a bit more pressing in ancient Greece than in Medieval Christendom.
3. WARNING: What follows should be taken cum grano salis since it may contain traces of peanuts. How's this for an apologetic for monarchy? Let's take as a premise that roughly 10% of a given population is really virtuous in the precise sense of being generally willing to act for the common good even against their own private good. The result will be that democracies will elect virtuous leaders 0% of the time while monarchies will produce virtuous leaders 10% of the time. Let me explain: in a democracy, people who are more interested in their own private good than in the common good will elect as leaders those who promise to provide for their private goods. The virtuous who would like to elect a virtuous leader will never gain more than 10% of the vote, and thus will fail 100% of the time. Arguing that 15% or 20% of men are really virtuous has no effect on the 100% failure rate. Only if one really thinks that 50% or more of the men of a population are virtuous can democracy function well.
In the case of a hereditary monarchy, however, roughly the same percentage of kings should be virtuous as of any other men, hence 10% of kings should be virtuous. Now whether one thinks that this percentage should be lower than that of the general populace because "power corrupts" or that it may sometimes be higher because of the thorough education in virtue that a good king will see that his son gets, and he his son, etc. matters little. Even on the most pessimistic view, a good king may at least once just happen to turn up, and in fact history shows us many examples of good kings.
The odds of having a virtuous king will thus always be at least 1% and more likely something like 10% while the odds of having a virtuous democratically elected leader will always be 0%. Therefore, monarchy is a superior form of government.