The Smoldering City upgrades are your long-term progression. Don't just pick upgrades randomly; have a strategic vision. Early on, prioritize upgrades that boost basic resource production, starting villager Resolve, or unlock new building types. As you progress, focus on upgrades that enhance specific species or provide powerful global buffs.
Consider which upgrades will best support your preferred playstyle or help you overcome challenges in higher-difficulty biomes. For example, if you struggle with Hostility, invest in upgrades that reduce its impact. If you rely heavily on trading, boost your Amber income. The right upgrades can make a significant difference in your overall success rate.