It seems that once you cross a certain threshold of cash that everything starts to snowball. I think it’d be nice if once you get to that point, you have to start acquiring other intangible resources in order to progress, and come up with some sort of plan about how to proceed. For example:
Political Capital - Obtained through: Campaign contributions, volunteer work (maybe a minigame where you drive around the city planting signs), buying gifts, provide services like food for campaign night, etc. Possible benefits: Decreased taxes, Ability to block a rival from opening a store, ability to evict a rival from a building.
Social Standing - Obtained through: Renting and furnishing high-end residence with high-end items. Buying high-end cars and yachts. Buying country-club memberships. Attending social events. Possible benefits: Access to new businesses and goods, protection from rival attacks, at high levels membership in a clique that allows you to control prices city-wide for certain goods.
Fame - Obtained through: Purchasing buildings, acquiring businesses. Holding press conferences to announce new business openings. Possible benefits: Free marketing for all businesses you own scaled to the level of your fame, hold press conferences to temporarily lower a rival’s marketing.
I think the best way to do this would be to have some sort of simple mini-game or some sort of activity instead of just pressing a button and spending money on the resource. The resources could also be intertwined such that in order to get a certain level of Fame, you have to have some Social Standing. Likewise a certain level of Fame would be required to get Political Capital. Finally you could introduce some Crusader Kings style events, where good and bad things could happen depending on your level of a certain resource.