I think that the US physics, and perhaps wider science, communities are starting to realise that they can't just expect to get the level of funding they previously did without further justification. Generally, and especially to politicians, that means demonstrating increased economic returns.

The UK physcis community has been going through this process for a number of years now, and seems to have convinced the politicians. Recent austerity budgets have not cut science funding anywhere near as much as other departments. I think the USA is just a few years behind in this respect.

I think there is a good case that funding "big" science generates economic growth. For example, here is a back of the envolop calculation of the returns on the 4 Billion dollar Investment in the Tevatron.

http://www.fnal.gov/pub/tevatron/files/120611Womersely.pdf

Of course, this is only a rough calculation, but it does give an idea of the argument "big science" must make to justify itself.

Here is another, much more detailed report, concerning the old synchrotron light source from the UK, which doesn't arrive at a final number, but does present a wealth of evidence supporting the argument that the payoffs outweigh the expenses.

http://www.stfc.ac.uk/resources/PDF/SRSImpact.pdf

They claim this is the first report of its type, but i would expect most large scale facilites will be looking to make this sort of case from now on.