"First, no one is sure aliens exist."

No one is sure aliens don't exist.
I am fairly certain that I have not seen any evidence of aliens existing. But even if no alien has ever visited earth within the last million years, this does not mean much in terms of whether aliens exist or not. There may not not be a single alien with 10 parsecs of Sol- it still doesn't mean much in terms of whether they exist

Second, mankind is already moving away from Earth...with machines.

Machines without any intelligence, machines comparable to an telephone answering machines.
If machines are not intelligent and somewhat independent, then machines will need instruction from earth [in your idea of things]- therefore they are confined by the speed of light. Unless one is confining oneself to the Moon- anywhere else in the solar system will have significant time lags.
One the significant values of the moon is being a hub to the rest of the solar system. With machines only one is devaluing one aspect of the Moon- one of machines only viable destination.

Now if we get AI, it's a kin to getting nanocarbon material a 100 times stronger than steel- such material would have far more value for use on earth rather merely for a space elevator.