Im going to speak about emblematic outposts of ancient era: the hitties and especially bantu. So the main trouble picking bantu culture is that at the end of ancient era you will lose 30 or 40 food as all outposts turn into regular one. Same can be said about money from hitties outposts. So, shall already built emblematic outposts of ancient era cultures stay after picking new culture?
(on the other hand there are huns and mongols, whose outposts don’t allow to build city, so for them it is okay to change back to regular outposts)

I agree on the Bantu, losing that much food really hurts your cities, especially if you haven't anticipated that it will happen. Fixing this might make them rather too powerful, so you would need to nerf something else to balance it I think. 

I still believe that already built unique outputs shall stay. Played one more time with hitties. It is very painful for your economic and strategic displacement to lose all this outpost abilities. 

EsoulBoy wrote:

I still believe that already built unique outputs shall stay. Played one more time with hitties. It is very painful for your economic and strategic displacement to lose all this outpost abilities. 

Also, they don't even give Influence with Liberty since they are outpost