I want to look at the productivity curves for each type of focus and the game implications.
We expect that average production per population is going to go up significantly over time so the player can build all the fancy new stuff. The steepness of this curve is something we will have to work out. I'll assume for now that it's steeper than linear.
If we keep a near-constant ratio of minerals:production, then the demand for minerals will follow a similar curve. Since we probably don't want to force the player to drastically increase the percentage of population employed in mining, this means the mining productivity curve should be at least as steep.
The amount of food consumed for each unit of population has got to be pretty constant. A person just doesn't consume exponentially more food as technology marches on. So what kind of productivity curve do we want for food?
1. A flat curve: This means that the percentage of the population devoted to farming is almost constant. It also basically rules out useful farming technology. If an omega-type plan is used, farm-world wealth will be basically flat while wealth of other worlds grows rapidly.
2. A linear curve: Farming population decreases over time. The main use of farming tech is free up population for more productive uses. Growing biomass to convert to minerals is not attractive late-game because mineral production is so much more efficient, unless conversion tech heavily favours food. Farm worlds dwindle in number and are still left behind economically, but not as drastically.
3. Same curve as industry/minerals: Farming population needed to support the larger population becomes miniscule over time(assuming adequate investment in farming technology). However, significant farming may still exist if diversion of biomass to support industry is researched. A single farm world could feed a very large empire, but if that world was captured/blockaded it would take time and much money to replace that food production.
Umm, more stuff along these ines is coming, but I should actually eat some lunch on my lunch break