I hope your aim isn't realism because what you've proposed is far less realistic than 'mana'.
Not to be pedantic, but it's actually exactly as unrealistic, since money could to be used in equally magical ways before in earlier installments of the game [QUICKLY, INJECT TWENTY FIVE MILLION DUCATS INTO 1444 GRANADA TO TURN IT INTO NAPOLEONIC FRANCE LEVELS OF TECHNOLOGY].
The problem with you guys' approach is just that you crunched together areas of government that didn't actually quite overlap as much, such as diplomacy, naval warfare, and trade.
Also that you kept the system TOO tied to monarch rolls when instead it should have been more like a general metric of government/social efficiency in various areas.
Also the technology/idea group anti-synergy.
Also the use of military points for general generation [what a fun thing to say].
Also using military points rather than manpower to supress rebels.
Also the fact that the advisor system is not very fleshed out.
And various other minor tidbits, probably.