In every strategy game there's the choice between building wide and building tall. Stellaris is the best example of this. People constantly debate which strategy is better.
In ThroB, there's no debate, building wide is the ONLY way to go. And here's why:
Level 1 buildings deliver 50% of the value of the chain. Upgrading a Level 1 farm to Level 2 costs enough to buy a small army, and with that army you can take a new Level 1 farm and double your investment. If you instead choose to upgrade, you get a measly 10 food and negligible income boost.
So spending cash on anything but the military is rarely worth it. I don't see the need to keep above 1K income per turn. The rest is better spent on the upkeep for bigger armies so I can keep expanding rapidly.