Add a new layer to economy and diplomacy by adding population companies based on political allignment. IE industrialist make mining companies, scientists make research stations, militerist will make starbases or pmc's etc. Have these companies seperate from your systems by using civilian ships. You could also request permision from allied factions to allow companies operate in their territories under an adjustable tax. Companies could be attcked by pirates and whether or not you help them adjust political approval. i that would be cool.