Well remembering all that took a while, so I didn't actually see your newer post before I finished.
If your kicking it out that far then no-one's can claim to make a stab based on anything other than guess work. So here goes
I'd guess that once most of the solar system is colonised and/or terraformed that's when asteroid mining is going to come into it's own. Loads of cheap fusion or cleverer power, funky hi-powered lasers or some clever anti-matter explosives to break the buggers up and robotic processing plants. Let's be honest with enough power to throw at a problem you can normally solve it.
Finally once you've gone to all the effort of terrafroming a planet you're going to want to keep it nice and clean, so planetery mining isn't going to be popular.
Asteroids
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