Rough calculations for the moon base/colony/mine for my nation (20k infra, 13k tech, agricultural resource set = 3 earth resources for Radon)
initial investment: 1.2 billion
additional (net) earnings accrued over the lifespan of the wonders: 4.0 billion
effective ROI: 233%
That's assuming 75% average hotspot efficiency, and the 90 day period it takes to get all 3 wonders set up for the first time has been amortized out.
Additionally, the profitable infrastructure limit increases from 20k to 23k, and the curve becomes fairly flat all the way to 25k. woo more soldiers!