Oh! Yeah, I figured out the saturation mechanic for areas, it makes sense! There's only so many trees in a forest, and seeing it grow back slowly between lives really sells that. I hadn't noticed the mines not regenerating. That explains why eventually my progress stagnated. I thought the mines increased the max it could refresh to, allowing you to go and focus on another task rather than babysitting it to avoid wasting ore. Since I eventually only needed iron for the tower, I had stopped making mines since I thought I didn't need the cap anymore. Maybe I'm misremembering, but it might be worth specifying that the 'rare rates,' from each mine apply at the masonry step. I thought it was a chance to harvest extra ore per operation or getting a different resource entirely.
Given that I was kneecapping my mines, the iron cost for reinforcement might not be as bad as I thought. I would have to play back through to there to see how it changes, but a larger workforce is a larger workforce. That might be worth it then.
Most of my time playing had the same basic objective each life, stocking up the resources I needed for the tower. The smaller tasks can usually be done within a life or two, so there wasn't much switching around for them. Preparing for the tower would get you enough resources to ensure 100% tool uptime, so the tool-giving hosts become a bit less important. I had just chucked a skeleton on each craft, with what seemed like reasonable crafting limits, one on berries, and then went with 3 mining, 1 chopping, and a hauler for each. Generally I would sit on the mines as well, again that was my only missing resource. The only lives that really impacted what I was doing were the beggars and foremen. Both have much shorter lifespans, so I would skip berries and go all in on something like processing any built up trees or ore. Generally I was preferring the traveler and geologist for their longer lifespans and the gathering bonus. Maybe I could have progressed a bit faster if I had engaged more with the skill distributions, but I figured I needed multiple different kinds of resources and it'd average out.
I'm probably gonna give it another go now that I know why my mines stopped producing, so I'll update this if tower floor one changes anything ere.