This really cannot be understated: if you are not Carthage and you want a functioning economy at all, you simply have to take this city. Period. I usually don't even notice it, but it was so stark in my latest campaign as Makedonia (on turn 350 at the moment). For over 300 turns I frequently languished in financial turmoil with periods of 20+ turns in debt or watching the "queues stalled" notice every other turn due to having limited funds. With an only modestly growing and often dramatically shrinking budget on a seemingly wild, sporadic basis, I never knew when the next crisis would leave me crippled as I faced hordes of enemies from four to five enemy factions all at once. Through sheer grit and determination, rarely auto-solving battles, I somehow managed to blitz the Mediterranean world and recruit enough troops to keep most of my provinces in the yellow or green territory while gradually expanding.
All of this has changed since I recently took Carthage. I wasn't quite yet done stomping the Romans, who still retained three provinces in Italy at the time, and BAM, the funds came in like a tidal wave for building new armies and naval fleets to combat the constant harassment of enemy fleets blockading a dozen of my ports. With the once daunting Carthaginian navy dismantled, I was quickly able to dominate the Mediterranean and the Black Sea, keeping Hayasdan at bay by defeating their fleets and turning the tables by blockading them instead. My funds have skyrocketed to a whopping 350,000 to 400,000 mnai on a rather consistent basis, even after building large ports and mines.
The Ptolemies have made the foolish error of deciding only now to challenge me again 30 some years after I took the Libyan desert bordering Egypt and Alexandria in the Nile Delta region (effectively kicking them out of the Mediterranean), and recently the Sinai from the Seleucids. It's a mistake that'll cost them dearly because now I have enough funds to just slop together an unstoppable train of huge armies and spam them into nonexistence with fresh recruits from all across the Eastern Mediterranean. I doubt the Ptolemies will exist by the time turn 400 rolls around, given the forces I've already arrayed against them.
Has anyone else experienced this giant economic boost after taking Carthage or some other important city? I noticed a little uptick after taking Alexandria, Pergamon, and Antioch, but they were incredibly modest compared to this. I'm basically an unstoppable behemoth now and it's so satisfying after dealing with everyone's annoying bull crap for so long.