If human beings are still biological creatures by the time we start
really colonizing space, then we should consider making other planets
more Earth-like.

My other suggestion is - if people still want to be organic as judging
by the reactions from film reviewers to the all-machine world of Cars -
to modify humans genetically so they can survive on chosen worlds.
Might be just a bit easier and cheaper than transforming an entire
planet to suit us.

If we could do that, then virtually any world would be open to us.

Maybe that is yet another reason why we can't find ETI in terms of
macroscopic structures: They have blended into their environments
so well through genetic manipulation that they are undetectable
outside their solar systems.

Then again, if we just take the Sol system apart for construction
materials, we could have a Type 2 Dyson Shell with the land equivalent
of five billion Earths.