Like I said in an earlier post, if all you are interested in is an immediate return in money (which I think is what you really mean when you say "concrete, tangible, material benefit"), then you are displaying the hallmarks and characteristics of a people well on the road to decay and decadence. When we place material comfort and monetary gain above all else, when we worship money as God, then we have truly lost our collective souls.
No, I can't tell you what discoveries will come of what we've learned so far in our honest and gainful efforts in space exploration and development. No more than Columbus could have foreseen the establishment of the freest and greatest nation the world has ever seen, when he set off to find a trade route to the East and stumbled upon some islands in the Caribbean. Nor could James Clerk Maxwell have foreseen the establishment of a vast and complex system of wireless communication when he took it upon himself to scribble down some equations on a piece of paper. Or those (taxpayer-funded) persons who labored in developing an electronic method of calculating ballistic trajectories could have foreseen the growth of a computer industry that would make calculating machines as commonplace in households today as radios and TVs were a few decades ago.
Like I said, think small, be small. Limit yourself to holding onto every penny you can, and pennies is what you will end up with when you crawl away to your hole to die. Meanwhile, others will forge a destiny in the stars. I just hope those are people of the great and free nations of the West. We can do it, if only we have the will and the vision to look beyond our own petty comforts.
I would like to point out something.. When we purchased the Louisiana Territory, there was controversy about the cost... When Jefferson funded the Lewis and Clark expedition there was controversy about the cost...
If it can NOT be applicable to anything even 10-20 years down the road then WHY is it being done?
"So that we know" and "so that we better understand" doesn't cut it anymore if there is no foreseeable use for the information.
If we cannot even live comfortably and indefinitely in orbit and get to and fro safely (as the current situation evidences) even just for the purposes of freefall experimentation then all the rest of it can be put aside until such time as its use is relevant.
IMO:
step 1) permanent Earth-orbit habitation WITH an iron-clad (and affordable) method of frequent transportation and supply.
step 2) the same goal around the Moon (obvious benefit of an orbital station first: rad shielding 50% of the time in orbit by the Moon's mass)
step 3) okay, NOW you can have an installation on the surface - a good place to work-out all the kinks expected in a longer-duration Mars mission (having an emergency 300k miles away is somewhat nicer than one around the opposite side of the Sun - you're only a few days from home)
God has nothing to do with it - He can ask His own questions if He has any.
Columbus was looking to make money and fame, and do it on Ferdy's & Bell's money instead of his own (the resulting syphilus epidemic was on-the-house).
Maxwell's early work dealt with the structure and behavior of Saturn's rings. His contributions to the study of gases is well known. His work on electricity and electromagnetism was based upon, and was an extension of, Faraday's theories. JCM only theorized about radio waves - Hertz discovered them. ALL of that: natural, observable, phenomena.
Regarding ballistics and computers: the computers existed. Is it any wonder that all kinds of things would be tried on them and some would consequently evolve the computer industry to what it is today? Manual ballistics calculators had been around for years (tables and slipsticks were used in both World Wars) and it is natural that the new computers would be used for faster calculations. Would computers have died-on-the-vine if the need for improved ballistics computations was nonexistent? Certainly not!
"Forging a destiny in the stars" is a pretty ideal; but there's a HELL of a lot of ground work that currently ISN'T being accomplished (and COULD be) to help humanity GET THERE.