Bobbywhy said:
The spin-off benefits from the manned space program are HUGE and IMPORTANT! I would say they are really relevant because they have affected our lives so much in so many areas, so should be included.
I'm not just a human space buff. It's my job.
That said, spinoffs from NASA's human space program have been neither huge nor important. There were some significant ones from the Apollo program, but those were low hanging fruit. Since then, the spinoffs have been on the order of better foam for mattresses. With one exception, focusing on spinoffs is the wrong way to go. That one exception is that human spaceflight has motivated lots of young people to pursue a technical education and later on pursue a career in some aspect of technology.
With regard to medical spinoffs, materials science spinoffs, or computer science spinoffs, investing in research in medicine, materials science, or computer science will give a much better ROI than giving money to NASA. With regard to aeronautics spinoffs, investing money in the aeronautics side of NASA will give a much better ROI than investing in the aerospace side. Expecting huge payoffs from what is at best tangential to NASA's human space flight effort is a fool's errand.
We explore space because we are human. It is our nature to explore. We explore space because there are huge potential direct payoffs (not spinoffs) from the resources this exploration will open up. It is also our nature to find and exploit opportunities. We also explore space because "my space program is better than yours". It's called soft diplomacy. Don't leave politics out of your equation. Except for some budding commercial space projects, space exploration is still funded primarily by governments. Politicians might not understand rocket science, but they do understand people, much better than rocket scientists understand people. Politics isn't rocket science. It's a lot harder.
We should not abandon human space exploration at this point in time. We are getting close to the point where a true monetary advantage to human space exploration is in sight. Just because our nation was at the forefront of human space exploration does not mean we will realize those benefits. It's those nations who see things through to the finish who will realize those benefits. China knows this. So does India. And so do our politicians.