As long as we are still leaving the planet in better shape for the next generation than we found it
We are? 
Considering the millions of hectares of forest lost each year, extinguishing species, overfishing, etc, I wouldn't say so.
Destruction of forest, extinguishing species, overfishing is a result of the inability to own these resources, not resource scarcity.
In any case, if we ever figure out how to mine asteroid...a single asteroid will be more than all the building, electronics, roads, and all the other material things that's made out of lead, steel, silicon, gold, etc, combined. Gold will cease to be the storage of wealth.
Assuming our population don't grow like rabbits and our hunger for resources don't grow like rabbits, it might be the all things that we will ever need for building anything.
The next question is how do we get enough energy? Do we get it from nuclear power on earth or absorb energy from the sun?
Not inability to own resources. Its the system that demands profit while theres no profit in preserving the earth.
Our population grows like rabbits. Our hunger for resources grow like rabbits but not directly because of what would be expected: population, but because 1/4 of the world needs more and more and more.
http://en.wikipedia.org/wiki/File:World-Population-1800-2100.png
About the asteroid. We don't even go to the fucking moon anymore because now its not a penis race and its not profitable. And your alarm clock could now be reprogrammed to guide us there.
About the energy, take a look at http://en.wikipedia.org/wiki/Kardashev_scale
There are three stages of civilization and we are not even in stage 1... the direction is clear.