Strategic Wonders

Sins seems primed for the addition of Wonders ala the Civilization series. You could have such structures provide influence as well as improve relations diplomatically either as a one time boost, an ongoing bonus to diplomacy, or a smattering of both. The existence of such in a sector could provide a boost to tourism and therefore trade of all sorts. Certain types could provide some sort of boost to research or to research of a certain kind. Some might provide a boost to artifact investigation (i.e. a royal museum).

Different types of Wonders might have different tiers of upgrade. Some might occupy space in orbit (at no cost in slots...) and be attackable. Of course, the attackable kinds of Wonders would be more beneficial than non-attackable ones.

Depending on whether or not such would be explored in the future, Wonders might help influence neutral factions to join your Empire.

Definitely something to ponder for the second diplomacy-oriented expansion.