Buildings of the wrong culture (After Conquest)

[krunsh]

This is something which has been confusing me for a long time, and I figured I might as well ask here.

I have been playing a Massilia campaign, and mostly conquering Gaul. This means that most of the buildings I get from captured towns are of the wrong culture (With the little alert symbol on them.). I am always given the option to convert them, which is extremely expensive... But I have yet to figure out if there are any penalties to not doing so?

Are other buildings any less effective?
Do they bring a cultural penalty?
Do they bring unhappiness?

The benefits of converting Cultural and military buildings is pretty straightforward and obvious, but when it comes to farm, industrial or civic buildings (Or even the Town itself.) it is somewhat unclear. This always leave me wondering if I should take over, pillage or sack a town (What is the most cost efficient, etc.).

Thank you for your time, and again for this amazing mod.

[Unactuality]

The most obvious reason is that they cannot be upgraded until they are converted.

But if you don't wish to upgrade them, I too wonder if there are any hidden penalties or other reasons for converting.

[Hoplitus]

I think there are no hidden penalties. Every effect a building has is displayed in the UI. Sometimes it might even give you an advantage if you get an enemy building into your own hands. I am just thinking of better horses of some barbarian cultures or better ship hulls of the Carthaginians which aren't accessible for e.g. Romans with their own buildings.
But if you want to further develop those conquered regions it is still better to convert or dismantle and build it all up anew.

[NYG 5]

I always thought they gave an added penalty to cultural differences/conversion