Thanks for pointing me to that thread. But I still suspect that some hand-waving along the lines of "the first few expeditions and colonies were not very successful, but then they figured stuff out with their magical dowsing-for-useful-resources apparatus" or similar could remove a lot of them.

Actually, though, that thread makes me think of how implausible most purely fantasy/sci-fi "and then they discovered an uninhabited planet/continent and started settling it and finding useful things in it" scenarios are.