NASA only receives about one half of one percent of the federal budget. There is a large national defense need for assured access to space. The ability to launch satellites is vital to national security. The manned spaceflight program provided an excellent venue for us to demonstate our countries technical abilities, without going to war. The space program is also a source of national pride. Icons such as the man on the moon, or the space shuttle are often the first thing that other countries think about when you mention the united state (well, at least they where, before we stared invading half the world). As far as the spin offs go, no they alone are not profitable, but there are many emerging technologies that nasa uses, and in the process, makes them practical for private enterprise to make profitable.
I would like to see more of NASA's activity privatized. The private space industry is finaly starting to be able to stand on its own. NASA, if used correctly, would serve of an excelent example of how through just the right amount of government assistance, a new private industry can be conceived, raised, and eventually able to be profitable on its own without government assistance. NASA should remain at the cutting edge of space exploration, and do everything in their power to open up the frontier of space to the rest of the country.