[Fyron]

After all this bonus stacking talk, I wonder: If a facility has a +40 bonus X/-40 penalty Y and then you have another facility tha has a +10 bonus Y do you end up with +40X/+10Y or +40X/-30Y? I assume it is the latter, which sucks

Now with Facilities, only the highest bonus is used; there is no stacking, sadly. Add a facility -500% minerals production and one with +10% minerals production to a planet, and it will get +10%, with the -500% ignored. You can still partially get the effect you want (assuming negative values actually work for these abilities, needs testing) because the planet will get the penalty unless you build an appropriate bonus facility.