In a since, similar to star trek, and each NPC race has their own specific bonus's and boosts to you.

In example,

1)The Draq are well renowned for their fuel depots, and having them in your empire is a real asset. (While this NPC race is controlled by you their Fuel Depot Technology grants you a 10 sec bonus to your energy recharge rate)

2)The Borellians are well reknowned for their engineers. (while this NPC race is controlled your ship and planetary defenses gain a 10% bonus to defense

3)The Yridians are well known for their Spy Network. (While this NPC race is controlled you gain a 10% bonus to cloak)

4)The Chalnoth are fierce warriors and are well versed in combat. (While this race is controlled you gain a 10% bonus to attack and a 20% invasion bonus)

5) The Vortexians are known for their micro-crystal technology. (While this race is controlled you gain a 10% bonus to scanning)

Different races give different bonuses.

NPC races can be on any size world, any type of world. basically it's an NPC controlled world with it's own Natural defenses and natural planetary bonuses when you conquer them. and it'll give us something else to fight over besides just resource rich worlds.

Hmm, that's a good idea. I like it. You could also hire crew members of different species to help you. You could hire say a Konqul tactical officer, who gives a larger bonus to damage than usual. Or, an Inergon engineer, who gives more energy than usual. More NPC races could be added too.