Especially combined with a few other prestige classes, like exemplar (take 10).. diplomacy, bluff, kingdom reputation... all like soft wax to be molded however way one wants to :p
Never mind they are no good at combat, but they can instead manipulate the whole kingdom, make every lil duchy want to join... and have those who are in dread the notion of seccession and how those seeking to break away will be known as babykillers and defilers of everything holy...
The perfect king, especially as they are less than useful in battle.