Asteroids are not all simple rocks, as spectrum analysis has revealed. Some have high concentrations of iron.
http://www.universetoday.com/37425/what-are-asteroids-made-of/
...and...
http://wiki.answers.com/Q/What_are_asteroids_made_of
My guess is that scientists are going after the metallic asteroids and NOT the rocky ones. I mean, duh! Right?
Next up is the economic benefit of a space station, which I will answer in the simplest, most abstract fashion possible:
Historically speaking, few things enrich a country more than exploration (The New World, Manifest Destiny, etc). OK, “war” is up there, too, but exploration is pretty high on the list. There is *a lot* to explore out there if we can do it in an economically viable fashion.
(I’m not even going to go into the scientific advancements that can enrich a country from a healthy space program.)
Agreed not all asteroids are simple rocks, but consider the earth and the asteroids formed form the same solar nebula, and look at the fraction of the earth that is something other than rocks. BUT let's say that 10% are nickel iron. Something - robot probe? - has to go to each and tell which class it falls into. So then you have to get the right ones into orbit, and then what do you do with a mass of nickel iron? You can make structural shapes out of it IF you have the right processing machinery. Any idea how much a plant to convert a lump of iron into structural material weighs? - A LOT!
There is *a lot* to explore out there if we can do it in an economically viable fashion
The key to your statement that keeps it from being hogwash is the phrase "economically viable fashion". Just how this can be done is a mystery that has eluded everyone on the earth so far. You are correct in that it is economics that drives exploration, but at the "astroomical" cost of returning space stuff to earth there literallly isn't any substance that makes it even close to break even. A giant boulder of pure platinum sitting on the moon would be too expensive to exploit (consider how much it cost to get the moon rocks.)
And as far as technological advances from the space program, These are few purchased at great lost opportunity cost. Private industry innovates ceaselessly (look at Apple) by diverting funds that would be spent in research on things that people actually want to space exploration,you DECREASE innovation in the private sector - trading it for giant engines and fuel tanks that shed chunks. (And alligator habitat)
The space program is just another form of corporate welfare.