Two planet species
All steps toward human habitation of Mars, including seeding an oxygenated atmosphere, are good steps. That's one place we can't stuff up, and hey, we might need a second planet one day. We should not be too afraid of diverting resources to such lofty projects. That and asteroid proofing the earth are probably the two most noble pursuits of science. If either of these things are acheived we are going to be around for long enough to achieve plenty more.