If you look at things over a broad span of time, things that are less important fall away. And if you look at things with the broadest possible span of time, with regards to the evolution of life – primitive life started 4 billion years ago – what are the important steps in the evolution of life? Well, obviously there was the advent of single celled life; there was the differentiation between plants and animals, life moving from the oceans onto land, then the development of mammals, and the ignition of the spark of human consciousness. And on that scale, I would argue that on that scale should also fit life becoming multiplanetary.
Life becoming multiplanetary is the natural successor to consciousness, because you need consciousness in order for a species to reach the point at which they are able to develop the technological ability to migrate from one planet to the next. This involves travelling millions of miles through irradiated vacuum, all the while living in an environment they did not evolve to exist in. We are currently living in just such a technological window where this may be possible, and we should exploit that fact. The window will not be open forever. All civilisations rise and fall, and with it, the abilities of that civilisation.
I think that if one can make the argument that something is important enough to fit onto the scale of evolution, then it is important, and maybe worth investing a little of our resources into. This doesn’t need to be a lot; it should definitely be a lot less than what we spend on healthcare, but maybe it should be more than we spend on lipstick.