Good point. Although relying on governor policies seems to expensive for a large empire.
Yes. The bigger question than what OP asks is generally under what circumstances you should spend influence to change a policy. This depends a lot on your play-style goals and priorities.
The point i try to make regarding this is that the dependability of a governor matters in this, because it lets the player estimate and have room to mitigateevents that affect the governor and the province - if they make this govenorship a priority, a governor can stay in charge of it for decades, getting value out of the policies the player has spent influence to assign.