I think it would be interesting if your own provinces were included in the opinion system. It could work as an abstraction of the internal politics of a country, and would bring your country to life in a simple way if you could see that some provinces had a better opinion of you (the country) and some provinces really didn't like you. Events and decisions could affect the relationships with your own provinces just as it will affect the relationships with other countries. Different government forms would have different bonuses and maluses with the provinces. A tribal government might have a real trouble to keep everyone on the positive side, and face constant revolts when opinions become too low. A feudal government would also have provinces with quick and sudden changes up or down to reflect that it's based on personal opinions. A republic on the other hand would be more stable, and only experience negative opinions from wrong culture or wrong religion provinces.
As a player you would have a mean of developing emotional connections to your provinces, and you would end up having favorite provinces that you cared about more than others. Your favorite provinces would be first in line to get that new building, and you would go to extra trouble in a war to lift a siege in one of your favorite provinces, while that pesky province that have always disliked you could get looted. Or, perhaps you will invest extra much in that pesky province, as a bribe to increase their opinion.
As a player you would have a mean of developing emotional connections to your provinces, and you would end up having favorite provinces that you cared about more than others. Your favorite provinces would be first in line to get that new building, and you would go to extra trouble in a war to lift a siege in one of your favorite provinces, while that pesky province that have always disliked you could get looted. Or, perhaps you will invest extra much in that pesky province, as a bribe to increase their opinion.