It looks to me, Luke, That if Mars (Which, in real life, is the next logical place of inhabitation) is thought of as a land of ghosts and superstition, then it is highly unlikely that planets outside of our immediate area are inhabited. And even if there ARE ships with interdimensional travel, By the looks of things, they are too expensive to give flights to enough civilians to inhabit a new planet.
I propose the following as a compromise: Earth is inhabited only. HOWEVER! With this interdimensional travel, people have found the planet known as Diamunde, which has oxygen and similar terrain to earth. As a result, they set up an experimental colony there to see if people could survive. Thus, there are a few hundred, perhaps thousand people in there.
The theory bieng that, if these people can survive here, then in the future, when dimensional travel ships arent so expensive, they can bring more people to inhabit the planet.