I checked up the wiki.

Is it correct?

Per Capita Income (PCI) 22.5 * (1 - Taxrate) * (1 + ((Networth/Land)/90000)) * (1 + (2 * (Ent/Land))) * BusTech * GvtPCIBonus

Does this mean that doubling my nw on the same land amount will approximately double the total cash generated before expenses?

It's a very small multiplier, and I believe it was changed to 18000. It won't double your net income, you'll get like a 5% increase in pci.

( 1+ (nw/land/18000) )

Didn't notice the part of 1+ the result of the division.

That seems like the most negligible bonus ever then.

Eh, I wouldn't say negligible. 5% more income is still 5% more income.

Tech gives free networth to bump that up. Wonder if an increase in military provides enough of a boost to offset the increase in expenses for that to be noticeable, or if there's an optimal range to maximize income by staying in a certain nw/a.. the 18k constant confounds me, why that number?

Surely for a reason. Also the drop from 90k->18k, I'm pretty certain that was a major buff to cashers, but I'm not good enough at math to figure it out.