I had all my main production cities building 'Lesser Wealth' for a time in my game. One or two of them still are (got Currency now but it's not as much help as expected - only 80% efficient in C2C). Yeah I'm struggling all right to balance the books - while trying to maintain 50% tech rate and keep up on espionage. I thought it was going to break the game, but it didn't.
Personally I could live with -150 per turn with a 3000 balance (ie. -5%). Not forever of course - I like to keep the deficit to 5% of what's left. Still that's only 50 per turn you need to find from building wealth. I also reverted to cheaper civics at one stage.
Decided to carry on and you were right there was alot I could do stay afloat. Was just feeling negative because of this unexplained cost increase. Sold a ton of workers and subdued animals, sent streams of caravans and traded a ton of goods to boost my gold as well as putting a few cities on 'wealth'. Got my costs down and my bank account is the healthest its been. Now back to those thoughts of war!!!