So long as you can see the income by city somewhere I think it is fine, you don't want to over load the main interface too much.
Instead I would work on improving the empire overview/ledger screens. For example I'm not all that taken with the city list showing my cities grouped by type, mainly because it means sorting is only between type and if I want to see which city has the highest/lowest value I need to check each group.
In this case I would like to have a toggle for whether the city list groups by type or has them all in one list
