Here's the thing though - we actually have not seen the impact of re-usability on launch prices. SpaceX's cost reductions to date have been purely in improvements to the manufacturing and test process, a willingness to take risks and the use of non-aerospace parts providers. Their launch costs are already rock bottom for the industry and they've only just begun reflying boosters. These boosters that they are reflying are already out of date - the newest version (block 5) will be much faster to recycle as they will require less inspections and tear downs. Because their costs are already so low they do not currently have to give big discounts on reflown rockets. That will come only when other reusable rockets from Blue Origin and China come on the market.
I think launch costs could go as low as $10 million with block 5 in a few years. BFR will likely break the sub-$1 million launch cost barrier. Currently launch costs for a large geostationary satellite are sitting at about $60 million, for reference. That's about half of what most other providers can offer. The Russians, Indians and Chinese can go lower but there are a lot of caveats with those providers I won't get into.
I do think the uses of outer space are relatively unknown right now. Resource extraction is the obvious low-hanging fruit but we have done very little research into in-space manufacturing. There will be all sorts of novel drugs, computer chips and super materials that can be made only in 0 g that we don't know about right now simply because it's been to expensive to get up there and experiment. The ISS was supposed to be the place to figure this stuff out but for a whole host of reasons it has fallen short to the point where the NASA office that coordinates research on the ISS has fallen under criticism for the under-utilization of the facility for research.
We are not going to find unobtanium in space. We will find instead invent new processes for manufacturing drugs and materials that are only possible in 0g that will improve life on Earth substantially. Eventually, as we build up our in-space industrial capacity (which is currently 0), we will begin moving down the economic ladder and producing more ordinary materials and extracting resources in space as it avoids all of the industrial impact and pollution that has thus far greatly harmed the Earth.
I do agree that there is nothing economically attractive about colonizing Mars until the colony itself develops an economy which is probably something that will take many decades.
