Space exploration has a well-documented track record of advancing technologies for us back on earth, and for a fraction of what some of our domestic projects cost.
http://spaceplace.nasa.gov/en/kids/spinoffs2.shtml
http://www.sti.nasa.gov/tto/Spinoff2009/pdf/Brochure_09_web....
I would guess that on balance, investments in NASA have resulted in a highly positive (direct and indirect) ROI for America and indeed the rest of the world. Perhaps the benefits aren't communicated as well as they could be.
In 2008 it's 0.6% of Fed Budget which is still a lot of roads. But more importantly: The NASA budget is larger than the National Science Foundation budget,[2] but only 61% of the National Institutes of Health budget. NASA does some interesting science but the focus is clearly on keeping the public entertained and not say lowering the cost to orbit which would be of great value.
Now, the technology transfer of government output to the private market, that's where the lowered cost and great value will come to the fore. I'm sure I'll rile the free market feathers by saying this, but SpaceX and Virgin Galactic would not exist without NASA. No way, no how.
Just to get you geeked out about NASA, though, here's a fan-made video on Youtube: http://www.youtube.com/watch?v=NXkuo1yihjs
Jersey Shore-style Fist-pumping science.
The government builds new roads to lower transportation costs.
NASA spent a less than 1 shuttle mission worth of funding to research scram jets over 7 years. Resulting in the X-43 which hit Mach 9.68 using an air breathing engine. , NASA Dryden engineers said that they expected all of their efforts to culminate in the production of a two-stage-to-orbit crewed Vehicle in about 20 years. However, the program was canceled, so, in the end you could be right
Still, scramjet's are one of the few technology's to be able to reduce the cost to orbit to 1/10th - 1/100th of current costs and instead people want to wast billions trying to build a moon base?
PS: The whole point of infrastructure is to lower prices. People could drive across the country before the interstate system, but it suddenly became cheaper and faster in large part because you could avoid stoplights and pedestrians etc.
That has happened occasionally (AT&T), but the more usual situation (Standard Oil, Alcoa Aluminum) is that prices go up, which isn't surprising since the main beneficiaries of "anti-monopoly" laws are the competitors who cannot compete with the "monopolist".