I think the biggest obstacle for anything like this to work would be the so-called R&D demand by the aerospace industry. Look how much was wasted on the International Space Station. There shouldn't have needed much spent on "research". Well, to prevent myself from going off on a long rant, the fleecing needs to stop so that the budget could be met.
It would be best to pick one objective and stick with it instead of writing a wish list. I would have focused on the moon. Yes, Mars has more of the resources required to support life, but the moon is right there! I saw it this morning on my way to work. Whatever research done on the ISS (that's not duplicating what the Russian learned on Mir decades ago) could be done on a much smaller platform.
The first trip to the moon might be one of the few government ran programs in living memory that actually earned a profit. The personal and corporate income taxes from software and microcomputer companies that came out of that technological revolution paid for the whole program at least once over. A moon lab might produce something similar. Technology used in recycling air and water could be used in all major cities to help reduce pollution (base case scenario there).
The thing to remember in arguing an economic basis for support for a space program is, the rate of profit needs to be
high. Space enterprise as such is quite risky. And investors are not generally after achieving the
average rate of profit--they are attracted by extra-high rates, and that is before factoring in risk.
Now the topic here is what sort of government-funded space project could the Bush administration plausibly have sold Congress in the late 1980s, one that would sustain interest in keeping up the funding over a decade or so. The government is not expected to acquire the profit; Congressmen are not seeking to (directly!) pocket the revenues. They are acting on behalf of corporate lobbyists whose firms do expect that. They don't care whether those revenues derive from the sale of real goods and services they have produced, or are simply extorted from the taxpayer and paid over to them in fees for products that contribute nothing to the overall economy--they are looking at portfolio growth.
But if the space program, for instance, is merely such a revenue transfer machine, the taxpayers who are not investors in the chosen contractor firms will have reason to complain!
You argue that the money invested in NASA in the 1960s doubled itself in a decade by yielding valuable new technologies that did augment the US (and world) economy. Taking that at face value, and assuming the full doubled return of revenues had already made itself manifest in the US economy as a whole, that averages out to an annual rate of profit of 7.18 percent. Now I don't know a lot of details about the prevailing rate of profit for US industries in the 1960s but I suspect that is indeed a very high rate.
But of course the picture probably isn't that rosy; if it were I can't see how support for the space program could have failed. The more concentrated that benefit was, the more stupendous the profits for the handful of enterprises involved; they wouldn't let it go; whereas if you are talking abut benefits diffused through the entire economy, then grassroots support for the program should have been very broad. Claiming the money was doubled--are you perhaps talking not about the period 1961-'71 but the entire world economy to date? That's not a decade, that's more like half a century, and the rate of profit is just 1.4 percent, which is dismally low. And of course with the spinoff benefits you mention spread out over the entire competitive capitalist world, the US share is even lower.
Arguing from spinoffs is dubious anyway; any technology that happens to have been first developed to reach a NASA specification could obviously just as well have been developed instead to solve the problems they are actually applied to in the Terran economy; it seems strange to argue that only a space program could have yielded them. If that can be shown to be true, it is more of an insight into the peculiar nature either of capitalism or the human mind itself.
Given the ideology of George H. W. Bush and his career profile, and of his party, one would think that a Republican space program in the late 1980s would be especially concerned to show the way to sustained and growing private investment in space itself, for profit. To do that, the government would be interested in demonstrating that not only average but high rates of profit could be earned by enterprises that produce goods and services stemming, not from spinoffs but from space itself. Perhaps Bush might have deemed it appropriate for the US government to assume and underwrite the risks of space travel, and thus elevate merely mediocre potential profits into more attractive ones. The spinoff factor might be deemed to offset the necessary high tax revenues this would entail.
But absent a clear notion that permanent and expanding human presence in space could reasonably be expected to open up opportunities for private profitable enterprises yielding higher than average rates of return, any degree of investment in space at all seems to be a frivolous luxury to the people who own most of the wealth in the Western world. It might be justified by military necessity or ambition, or simply be an indulgence--but never one on a serious economic scale.
Vice versa--if there is a clear and solid case to be made for substantial and growing profits to be made in space enterprise, than programs as grandiose as half a trillion dollars and even more would be quite well justified--and would be supported tenaciously by both the small but wealthy corporate sector that hopes to double-dip (taking in profits both from servicing the government investment, and then later from ownership of the profitable space enterprises) and the general public at large, making it political gold.
I leave it up to others for now to debate whether these glittering economic prospects exist and our government and those of every other nation in the world have been too foolish to seize the opportunity, or whether space projects even at a tenth or less the cost NASA put forth in 1989 die in the conceptual phase because such opportunities either are extremely risky and speculative, or don't exist at all.
iloted Mars Flyby/Gia Sheild Piloted NEO rendezvous 
