I wrote an essay once that explored this subject. To my surprise I found a great deal of research suggesting that the economic benefit of government spending on basic science was pretty negligible. A bit like this:
As B.L.S. (US Bureau of Labor Statistics) economist Leo Sveikaukas found in a 2007 review of the literature, “The overall rate of return to R&D is very large…. However, these returns apply only to privately financed R&D in industry. Returns to many forms of publicly financed R&D are near zero.”
Of course this doesn't mean we shouldn't spend money on basic scientific research just that we can't justify that spending on the basis of economic benefit.