you still haven't explained how private investment will get any return that compensates for the hugely expensive outlay.
I did. NASA, a US government agency, has no means of reaching orbit itself and must turn to companies like SpaceX. STS (the space shuttle) was a boondoggle and did essentially nothing
to return on the investment. In fact, NASA is busy selling off hardware and launch complexes. (Reiterating what I said earlier, governments spend/consume, they do not invest.) Elon Musk has much larger plans for SpaceX than merely getting to orbit. For now, the company can sell that service to those who need it. Some customers may have other money-making enterprises, if they can just get to orbit, or farther. The Mars article in the OP suggested nothing that has not already been done in Apollo and other missions. That's hardly visionary. "Three people set foot on Mars! Yay!" Now what?
SpaceX may be operating at a loss right now, but investors (like Musk) usually have several other irons in the fire at the same time. Steve Jobs ran Pixar at a loss for years because he had a vision of what it could become. (It was part of a long term trend to sell "content," as well as the machines to run it on.) The long investment was necessary because the company was venturing into an entirely new field. It paid off so well that the rest of the industry started shutting down their 2D and traditional cel animation departments in a knee-jerk reaction.
There are many companies reaching for space right now, and only a small portion of them are rocketeers. That's because there is money to be made. The visionaries of the 19th century rebuilt the US after the Civil War with trains, power and steel. The visionaries of the 21st will take us off-planet. And they'll make a lot of money doing it.