It is always good to have backup plans, but right now, a backup plan for if they do work out seems more important. The issue is not that we wouldn't have more resources in the future; of course we will, one way or another. Even without robotics, we will rather soon find ways to rejuvenate people, we will have all kinds of productivity increasing technology, we will have access to raw materials from around the solar system.
But the real question is: How do we organize the distribution of all that wealth? Will a few rich people get all the profit? Or will we make sure every human being on the planet gets a fair share?
Bezug.