I have to agree with Dony, upgrading culture buildings from the pond to the orc's building will result in less culture overall, which is not desirable. I never go for the culture building with more culture per square if that building gives less culture than another bigger building, because you have to take into account NH and how it affects your culture.
we have a very limited amount of NH, so its best to have the least amount of culture buildings to be polished as possible, to maximize the gains, which means going for the building with the most overall culture value, and not the highest culture per square value. It is disapointing that orc don't offer us such a building... it looks like its inno once again wanting to force players to invest in premium buildings and this time its not even for the added pop, its just to be able to stay afloat culture wise.
upgrading the pond to the campfire will mean a loss of 1600 culture per building (800+800 from NH) and the space you get back its not worth the trade off, as you will end having to build more campfires to make up for the loss.