So I started the quest Hard Luck Blues (which lets you into Vault 34). Is there any benefit to giving the occupants control versus shutting down the reactor?

Hummph no I do not think there is... you get a bit of goodwill from Ncr if you close the vents.. both give you exp. But i was thinking (now where it is too late for me to backtrack heh) since i decided to rerout the terminal.. that the survivor family in the vault that wrote the note are most likely long dead or ghoulifed and even if alive doomed to become molemen or somesuch as they will never be able to leave the vault?? heh

I've been wondering about this one too, initially I saved the family but got no feedback, I searched around the vault then went out in case they were escaping another way .. nothing. So I loaded back to before flipping the switch, raided the armoury for the All-American (Looks like a special m4a1 with comabt optic) and left it for now. Anyone found the family? I was expecting the water level to drop again or something.