Platinum's principal use is in catalytic converters, which with the demise of the petrol engine in the, hopefully, not too different future, may become significantly less valuable.
Platinum has other uses, especially in fuel cell membranes, which could be in high demand in near- to medium-term future.
Water they suggest could be used to make rocket fuel. Except that the amount of energy needed to separate it into hydrogen and oxygen would seem to make this a rather extravagant notion. Surely water in space would be most valuable as...well...water?
No, you don't understand it.
Water in space is precious because it's already in space. Launching *anything* from Earth surface to space costs a lot of energy, and therefore money. Basically sending a kilogram to low-Earth orbit costs the equivalent of the mass in gold. Worse, reaction rockets using liquid hydrogen (LH2)-liquid oxygen (LOx) are bulky because of hydrogen's low density. Even worse, LH2 is VERY difficult to store for long periods, because this stuff will evaporate from about anything unless frozen to near absolute zero.
Therefore, getting water in space and producing rocket fuel from it there could potentially be very lucrative and far less expensive than having to launch all the propellant from Earth. The energy cost of breaking water molecules into LH2/LOx is trivial compared to that, especially since solar energy is abundant in this corner of the Solar System.
That's the point of looking for water on the Moon or the Near-Earth asteroids. The costs in energy of transporting it from these locations to low-Earth orbit are far lower than the alternative of launching it from Earth.
I admire these people's vision. I can see nothing wrong with looking forward. But are they being realistic, or just appealing to the gullibility of the average likely investor with more money than sense?
That remains to be seen. If nobody tries, though, we'll never know.
I understand that getting your materials in space for use in space makes a lot of sense. But the difficulties abound. It would make no sense to bring this stuff back down to earth, manufacture it, and then send it back into space. So not only would you need to mine the stuff but also manufacture it out in space.
Bringing stuff from space back to Earth does not make any economic sense at all (unless you want to sell Martian rocks to collectors or soil samples to research organizations) and that's how it's going to be for a long time. That's not the point though - what we want now is to get the stuff we need for endeavours in space
in space. This way we could reduce the costs of government and private space efforts considerably. Whoever manages to succeed in this will also make money on it. It's like going on a long hike - if you know you can get water and food mid-way, you don't have to carry all of it with you in your already heavy backpack.
It's a bit frustrating to read when I have so many things I could add/comment on/correct/etc. 
