I would like to put forth a suggestion, slightly modified, which Don E had from the royal library, to change the Rule Province action.

A province has two numbers associated with it, province level and points towards next level. A human province needs 3xfuture province level in points to go up 1 province level.
Each spring every province goes up 1 point.
Raiding a province or an occupying army can can damage the number of points a province has, and if points drop below 0 a provinces level goes down. A 4(2) which loses 3 points drops to a 3(11), one point less than is needed to become a 4th level province.
Mustering a unit from a province takes away a point, while succesfully disbanding a unit in a province adds a point.
A rule province action can add any number of points a regent wants. The DC is 10 + 2xpoints to be added, and costs 1 GB per point. A rule province can also be a realm action, following standard rules.
Other races have a different points/level ratio. Goblins are 2/1, Dwarves 4/1 and Sidhelien 5/1.

The pros are more realistic. Makes the time and GB needed to raise a province levels greater, but also means that so much isn't going to ride on one role when it comes to higher level provinces. It provides a greater role for raiding and occupying provinces over the long run, as enemies can get more golden eggs out without destroying the goose.

The main con is that it is much more complicated, and maybe not worth the effort. Though I would add that a simple spreadsheet could greatly simplify it, especially the yearly increase.