The US Space Program is possibly the only Government program to ever pay for itself. The returns to the economy in the form of jobs, new technology, etc are incalculable. Spin-offs alone are the basis for most of the advancements in computers, medical technology, food storage, metalurgy, weather prediction, communcations...
Do you have a cell phone? Thank the Space Program.
Do you watch Digital TV? Thank the Space Program.
Do you own a computer? Thank the Space Program.
Have you or anyone you know ever had a serious medical problem diagnosed with a CAT Scan or MRI? You quite literally owe a life to the Space Program.
You can't judge the value of something based on simple cause and effect. You HAVE to look at the secondary and tertiary effects to see the true cost or benefit. The early Space Program didn't pay off directly but the spinoff technologies the Mercury, Gemini and Apollo programs gave birth to are still growing and paying dividends today. And they'll continue to do so for the forseeable future. The Space Program, especially now that it's privatizing, is money well spent.
Just my .02 worth,