Though, the point I made stands: In the case of either alien species, the need would not exist.
Except that in the new series, we don't yet know why the aliens are at Earth (though the promo for next week's episode claims their purpose will be revealed -- but promos aren't always trustworthy). Despite their cover story, it might have nothing to do with the acquisition of resources. In fact, I have a hypothesis about what their real purpose is, but this isn't the place to discuss it.
We already know that the V's (at least, not the spies) are all addicts to some "Bliss" that integrates them all.
I think they are fleeing. . . something