In my opinion, if you add a buildable market with an exchange rate to the fourth game, no one will build it because it won't be profitable. And the principle of "want to trade - spend a day" would be completely inappropriate.
So maybe it's not that the exchange rate is too cheap in the fourth game, but rather that it's too high in the third game.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!