Strictly speaking, the economy isn't limited to the planet any more. We're already doing stuff outside the biosphere. We haven't yet been able to bring resources in from outside. Within a decade though, we'll be importing solar power from space. Within a couple of decades, we'll have some space manufacturing using processes which require zerogee/lowgee facilities. Within a few decades, we're likely to be mining space-based materials, though most likely to supply space-based infrastructure for some decades after that.
The main point is though, that we're not limited to just one planet any more.
They would to be shipped back directly to Earth, yes. Current deltavee costs for a mission from Earth mean that even were the Moon covered in a layer of cut diamonds and all you had to do was take a bucket and spade, you couldn't run it at a profit. Economically speaking, the only thing that currently looks in the ballpark of qualifying is Helium 3 mined from the Moon for fusion reactors on Earth.
I'm optimistic though that even if the Giant Government Bureaucracies continue to launch missiles at the Moon, private industry will be forced to build spaceplanes for tourists. Eventually that will get weight cost to orbit down, and once you're in orbit, you're halfway to anywhwere in the solar system in deltavee terms.
Nevertheless, apart from some oddities in microgee manufacturing that we can't do on Earth (optics and materials look most likely) material resources harvested in space or on other bodies will be used entirely to supply and resupply bases and infrastucture in space, mainly because it costs a hell of a lot to loft them from earth. First use will be mining lunar regolith to cover a lnar base and at as a radiation shield. Sooner or later robots will mine Mars to make fuel for visiting astronauts to get around and even to get back to Earth. The only real import to Earth for a while will be solar power beamed down from solar power satellites.
In the longer term, some of the exotic carbon materials are only an order of magnitude short in the strength needed to put up beanstalks (lifts to geostationary orbit and beyond). Once we get those up, space is just a rather tedious lift journey straight up and down. No doubt the first guys to build 'em will do about as well as the Channel Tunnel folks, but when their initial bonds collapse and they go bankrupt, costs to orbit will fall dramatically. After that, the solar system is our oyster.
The galaxy will take a little longer. Space between stars really is kinda big.
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