I think, but i cant be sure, they lower aip twice as much if you liberate them. (they do it once on the x:01 mark, and again on the x:yy mark where you liberated them)
edit:
Although yes, the wiki changelog states
In the prior version, the Civilian Leaders outposts were not working properly -- they could not be captured by taking their planet. Now they are properly captured, and they also give positive AI progress even when the AI command station has been destroyed but the humans have not yet colonized the planet.
and
Up to 10 Spire Civilian Leader Outposts are scattered throughout the galaxy in the control of the AI. Against their will, every hour each outpost increases the AI Progress by 1. You have the choice of either destroying these outposts for colloduing with the AI, or freeing the outposts by capturing the planet from the AI. When freed, each of these outposts will gratefully decrease the AI Progress by one every hour.