The mind-buggering scale of astronomical distances also rapidly squelches any thought of sustaining economic growth into the medium future. Given the most ridiculously generous assumptions - like empty space having the energy-density of solid lead! - the volume of space we would require to provide us with energy starts to expand faster than light in an absurdly short time. (About 4,500 years given the latter absurd assumption and only 2% growth.) When you consider the actual staggering emptiness of space and the expense of getting off the Earth, even exploiting much of the solar system before growth is stalled becomes a stretch. Sooner or later (actually sooner) we are going to have to learn to live with what we have here at home and not too much more, give or take possibly a solar power station or two in orbit and a few minerals from the moon.

One noble exception to the rule for SciFi which I would like to mention is Greg Bear's Queen of Angels. In it, he considers the psychology of a robotic space probe advancing towards Alpha Centauri and evolving towards self-awareness in the midst of the terrifying emptiness of interstellar space. If we have a future beyond the Oort Cloud, I suspect it will be of this form.