Small and easy suggestion:
now I'm playing without espionage.
So all espionage buildings give cultural bonus in coeff 1 = 1.
It is too much overpowered when "brothel" add +25% culture, or "meeting hall" add +15% culture. It is too huge bonus for such cheap building.
I suggest to change
"NO_ESPIONAGE_CULTURE_LEVEL_MODIFIER" from 100 to something like 20.
Then brothel will add +5% cultural bonus, meeting hall - +3% and it seems not overpowered.
More logical will be change it to 0, because: why brothel adding culture? If city has 200 culture per turn, why brothel add three times more culture then theatre?
But I don't know about problems with that: may be AI will build espionage buildings anyway and it will do game too easier for human.
P.S. The reason that I don't like espionage because it is adding too much microcontrol without compensation. I like the part when you steal technology and change civics, but I think it must be only one panel when you spend you espionage scores to what you want. Without many additional actions of train spies, driving them to cities different marshroutes ( often naval transport, so you need to construct ships, load spies, unload spies, ufff) , waiting 5 turns etc. It is microcontrol without real affecting of gameplay so it is redundant. I'am dreaming of creating mod with that changes.