I've always been a fan of space exploration, which means I've often gotten into arguments with people over the value of doing it. NASA (among others) spends a lot of its public-relations budget promoting the importance of exploring space, but I think they focus on the wrong things.
On the NASA web page there's a whole section on "Benefits to You" which emphasizes the important and helpful "spinoff" technologies first developed for space exploration. It's a nice idea, but it's kind of wrong-headed, in my opinion.
After all, a critic might point out that the same technologies might easily be developed without the additional expense of doing space exploration. If NASA is studying sleep to help astronauts aboard the ISS, they could just as easily do sleep research without a space station.
The fact is that any large technology enterprise will generate spinoff devices and applications. We could be spending NASA's budget on digging a giant hole in the ground, and that would produce useful innovations in excavator and pumping technology. The fact that digging a giant hole might produce some incidental benefits doesn't justify doing it.
I think NASA and other space advocates should put more effort into justifying space exploration for its own sake. The Earth is a tiny part of the Universe. It's a tiny part of just the Solar System. If we restrict ourselves to just learning about the Earth that means we're ignoring the other 99.9997 percent of the Solar System. That's like focusing on part of one square foot of a field covering an entire acre. That square foot may be important to you, but the acre is likely to hold other things which may interest you, or be of value. You can't tell until you walk around.
Instead of holding up a can of Tang or a Teflon skillet, space advocates should be turning the tables on people who question the value of going beyond Earth: how do they know we won't find anything of importance? You can't know until you look!