If we are going to cite ancient philosophy, it's worth mentioning Plato's Republic and the 5 forms of government. Through careful argument he makes a pretty good case for an aristocracy: Plato's five regimes
Read the actual book since it relates the individual characteristic to a collective state. Its also very important to distinguish between a constitutional monarchy and a absolute monarchy, the former being a sophistication of the latter, yielding a better form of government.
The advantages of having a monarch in the traditional sense, is that he or she is incorruptible; because he or she is born with the power, and therefore does not need to grease the palms of people to gain more. Even in some kind of meritocracy, individuals will have to grease the palms of the corrupt to gain power and this is clearly articulated in The Republic.
The benefits of a constitutional monarchy is that the monarch compliments the elected head of government. One is a safeguard to the integrity of the other.
Now for some facts and empirical evidence since this will shed more light on the case for a constitutional monarchy. Take a look at the top 10 most prosperous countries in the world. 8 out of the top 10 countries are constitutional monarchy.
Secondly, give me an example of any country that has replaced a constitutional monarchy with another form of government, and come off better. Doesn't exist. Even abolishing absolute monarchies has caused more problems than it has solved e.g Afghanistan, Libya, Ethiopia, Iran. All had more prosperous, cultured and progressive societies before the monarchy was killed. Russia, arguably another example, and England during Oliver Cromwell became worse off, the latter form of government resulting in the death of millions of Irish. So IMHO it's about progressing government that is proven, not revolution or change for the sake of change.