Hm, I may be in the minority here, but I think we should do it. Namely once you have the ability to become a 2 planet species, you really should. Mankind has spead so far and is at capacity and over in many places on the planet we're on. I see this going one of two ways, either we find more land to put people on, and more resources for the expnded population, or we're in for more wars and killing over the land and resources we still have remaining. There is of course still the possiability of globial castrophies, of both man made and natrual causes, which makes having a secondary home for our species a wise option.
Is it expensive, of course, but so is going extinct because of inertia.