The space program, for example, has resulted in lots of useful product spin-offs, but almost nothing that could not have been discovered independently without spending billions on a manned space program
If this site:
http://www.vectorsite.net/tamrc_24.html is worth anything, it didn't do even that:
"In contemporary dollars, Apollo cost $25 billion USD, and at its peak it accounted for almost one cent on every dollar of US economic output. Apollo funds similarly totaled about 20% of all US public and private research money at that time. In 1971, NASA commissioned a study that claimed the Apollo program generated a $7 USD return for every dollar spent. The impartiality of such a study was suspect, since NASA used it to justify their funding requests, and the Congressional General Accounting Office (GAO), never much of a friend to the agency, was highly critical.
There was also the question of how relevant such a statistic was even if it was true. A critic could easily observe that to justify the Apollo program only in terms of its incidental benefits and not on its own merit was to imply that it had no merit in itself. States with industries and centers that were the beneficiaries of Apollo funding, such as Florida, Louisiana, Alabama, Texas, and California, of course obtained an economic benefit from the work, but could the money have been better spent?
The US interstate highway program, another huge Federal project, also boosted the economy through government contracts, but the end result of the interstate highway system was an "infrastructure" that was directly useful to the vast majority of American citizens, and by even conservative accounting exercises paid back its investment many times over. It is difficult to identify similar long-term benefits from Apollo. The specific technologies developed for the program, such as the Saturn V booster, were more or less abandoned later. While manufacturers used the publicity hype associated with Apollo to promote "space age" products such as Velcro and Teflon, these products had been developed long before. Teflon was actually discovered, more or less by accident, in 1938, and had been used in chemical processing for the US atomic bomb project in World War II.
The only major consumer products to obviously owe their origins to the Apollo program are cordless tools. The Black & Decker company had won a contract to develop a lightweight portable drill for the Apollo program, and promptly developed and delivered it. The company thought they could leverage this effort into a commercial product, and in 1974, Black & Decker introduced a multifunction portable tool that could be configured as a drill, portable vacuum cleaner, and a hedge trimmer. The product died in the marketplace, since nobody had developed low-cost rechargeable batteries that had acceptable lifetimes. The Moon drill itself had used high-grade silver-zinc batteries that were too expensive for a consumer product. It wasn't until 1978 that General Electric was able to provide Black & Decker with rechargeable batteries that could last from five to six years, and in 1979 Black & Decker introduced the popular "Dustbuster" cordless vacuum cleaner. "
I would defend Moon program on the argument that it *made entire humanity more ambitious and feeling less constrained on this planet*, but not even on basis on producing usable technologies as side effects.