I was just thinking about how getting a kingdom to 4 stars has a very low incentive, other than to power it through to 5 stars. It would be nice if there was a more important reward than +50 gold. While this is a permanent daily bonus, you can easily get 3k gold in a single PvP match. Anyone with a 4 star kingdom is likely not in dire need of more gold, at least not such a small amount.
I would suggest a change to the 4* bonus, such as
150 gold (still not great, but it least it’s a proportionately improved reward for the difficulty involved in getting a kingdom to 4 stars)
1 random traitstone (for people who have 4* all kingdoms this could be OP though getting an average of over 4 traitstones every hour for a fully maxed kingdom)
10 glory (glory is the most coveted resource, and an easier way to get glory would seem like a much more satisfying reward when leveling up something to 4*
5-10% chance of a “double” tribute, which would stack with the 1 gold star bonus and home kingdom bonus if it happens to trigger on your home kingdom.
1 glory/gem key each time the city tributes (even a gold key would be an improvement over 50 gold, but not nearly as exciting as a glory/gem key)
Alternatively, maybe there could be some separate system that takes the total number of stars in your kingdom that could provide an added incentive to 4*. And yes, I realize that the 5* bonus is REALLY good and there will probably be people out there saying that the 4* reward isn’t great because the 5* is so good, but I would disagree that we should throwaway the 4* bonus to a mere 50 gold just due to that fact