Well, i am making a chain of zero maintenance buildings that provide small effects and work in a tree, based on the Palace Additions mod... The bonuses are "small" or a little less than normal low-tier buildings. The ladder is:
Palace Alter, +1 happiness, +1 faith > (cost 60, hurry cost 30)
Great Hall, +1 happiness, +1 culture >
Palace Gardens, +2 food >
Palace Observatory, +2 science >
Labor Hall, +2 production >
Palace Treasury, +2 gold >
Palace Throne Room, +1 faith, happiness, gold, culture, production, science
This would follow the footsteps of it's predecessor and have no tech requirements or maintenance, but have about 20% more cost to produce/buy.
One difference, is the original mod gave you much stronger bonuses, one level gave 2 free workers and another gave a free great person - which i will not do.
I am getting close to finish, actually...