
When I first started playing Skyrim I used to have a mod that added a thanes' hall outside the city walls, I could go there to get followers to help in my quests. If modifying the city sounds too complicated, you could just focus on building up the Whiterun thanes or all thanes as a faction. This mod author is doing something similar for Windhelm and Riften. Maybe they were irregular units allied with the Stormcloaks. But I have completed a battle with the other thanes against a suspicious band of thieves and cutthroats using catapults and battle animals (elephants and sabercats). Having only just started playing it, I am not sure how far its quests go. Balgruuf's thanes work on his behalf to defend Whiterun. Beside expanding the city's neighborhoods, CWE adds more thanes to the city. The mod Capital Whiterun Expansion does something like this. Holding court is pretty boring compared to fighting dragons, bandits, or traitors. But being a ruler of a city or province limits mobility if you play the role right. Keeping the Dragonborn as a thane would enable him/her to go anywhere and do anything on Balgruuf or the Greybeards' behalf. To me, the Dragonborn should be more of an adventurer than a ruler. But don't think deposing Balgruuf as jarl would do that very well.

I agree that much more could be done to make spending time in Whiterun worthwhile.
