for all of food/gold/oil there needs to be an end-game 'sink'... something to do with them once you're developed with full walls and oil productions done.
what we *really* want is some way of converting them to crowns .... but even just diamonds ...
perhaps maximum capacity gold or food for a diamond, maximum capacity oil for a crown?
playing devil's advocate, nexon would call *general upgrades* the oil sink, since that's a lot of oil for practical strength.
there is a kind of mechanic for crown farming..... put your mills/markets outside your walls but near defensive structures ..
allow yourself to be raided, but shoot down the raiders .. "farming" crowns off of attackers.
as a practical matter, i get more crowns doing this than i'm likely to get exchanging them for crowns if such a thing were set up.
so, if you're full on food/gold set up a kill zone next to mills/markets on your border.
oil is trickier since the refinery is an easy target; i think it's better to keep it inaccessibly central and it serves the same purpose.
