I think it's about half.A merchant republic with a high learning mage on the Imperial Isle is generally a nightmare though since they're likely to get advancements faster than most other characters and the White-Gold Tower is basically guaranteed to make you a force to be reckoned with in Cyrodiil both militarily and economically... Which is nice because most of the people you could put in power anywhere won't be upgrading their own things for a while. Also, I don't remember if this is correct, but don't you only get back part of their wealth when they die or am I thinking of a feature that was unique to one mod?
OF COURSE, once you've slapped trade posts with smuggling dens all over a trade route, you're still going to be raking in 100 a month, which dumps enough cash into your dynasty's hands to still amount to a insane amount any time one dies.
Once the continent is under my control, I'm going to go on a seduction spree....