Currency layer

Currency (money name, face and exchange rate) could be another mechanic layer similar to culture, religion, etc.

Currency layer requires certain technologies and/or cultural levels to kick off and progress.

Afterwards currency has it's own progression tree allowing you to tweak it for flavour and profit (make it minted, printed, tie the value to mineral or another equivalent, go cashless, go crypto, denominate, allow to use abroad, protect with watermarks, holo, RFID). There could be a small generator allowing to choose a style of your notes out of layers of pre-made elements - let players share their crazy violet zebra bills on the forum.

Currency layer acts on it's own, but could be affected by other layers (like spreading/stopping with certain cultural and/or religious traits).

Financial districts and/or individual buildings strengthen affect currency layer by providing currency advancement points and/or directly helping spread the influence.

Diplomatic treaties such as alliances might involve using a common currency.

"Strengthening" your currency should result in either/or adding to your financial capacity (alternatively by lowering building prices) or converting to final score thus making finances an [indirect?] winning condition.

I so far failed to find any other game that did that mechanic, but why not? We all use money every day and a lot of times have to exchange or track inflation, or see another cryptocurrency bubble explode. Let's ampliify this (safely in-game)!