I have to say that this is one of the think I wonder about DW. I just played Saxony (a now 4PM, but in a big country, it would be strange to not be able to construct new buildings. Magistrates is an interesting things, but it could be like manpower (with a malus when you have too much of them (ineficient bureaucrats)).
I'd like to have a "magistrates slider", that scales with nation size, tech and government. A full slider with a globe-spanning empire should cost one arm, one eye and liver. :3