I think I'd estimate this at <1%, but I don't want to tie up my mana for 40 years.

Venus is hell. In the unlikely event that it has some very valuable resources we can't get anywhere else, we'll be mining them with robots.

@Fion The loan system mean you get your mana back after some time (not quite sure when).

Also, I want to make it clear that this doesn't mean that humans need to be on the surface. In the atmosphere counts.