Interesting results from an investigation commissioned by the British Library trying to put a value on the benefit to the UK the library delivers. I saw a news report about a study that was carried out in Boston a while ago where (nine, I think) Universities reported that the economic impact on Boston of their presence in the area was the equivalent of holding an olympic games there each year. I don't know of other library studies quite like this, though, although I assume some exist.
The study shows � taking conservative estimates � that for every �1 of public funds the Library receives it generates over �4 of value to the UK economy. In addition, the findings show that the Library adds �363 million of value each year � �304 million indirectly and �59 million directly � and that, without the Library, the UK would lose �280 million of economic value a year. [Press Release - �363 million a year knowledge dividend to UK economy - UK national library reveals results of ground-breaking research]