Instead, do you think at pop 200, the charisma of the radio operators could be turned fully to making the current dwellers happy? At least until the Deathclaws make re-population necessary because you can't afford to revive all the dead.
I just leave enough space to send newcomers out to die. It only takes a couple of hours for the wasteland to kill them, plus there's a chance, if your game glitches, they'll suddenly find super rare items and you can recall them and collect.