Why Space Exploration is Worth It

Last night, NASA pulled off a brilliant landing of the Phoenix lander, our latest visitor to Mars. Scientists held their breath as they waited to hear whether the $325 million project had succeeded. When that much money goes into a "cheap" project, one has to ask: is space exploration worth it?

Yes, because of the long-term benefits of space
Investment in space gives us the research and experience we need to build safe and innovative space travel. The information returned on Mars's polar caps is crucial if we ever intend a round-trip visit. Mars, the moon, and asteroids have natural resources which can be strip-mined with no Earth-killing side effects.

Yes, because of the effects of space research
Space research was recognized as the forefront of global technology during the space race. It continues to have a strong role on our daily living and work. (search for NASA spinoffs)
In addition, a good deal of the Phoenix project was done by students at the University of Arizona, who now have the experience and drive to apply their work in the aerospace field - building the next airplanes, fighter jets, and spacecraft.

Yes, because we want to meet our neighbors
While humanity is the unchallenged intelligence in our solar system, there could be itty-bitty bacteria in the ice of Europa, Mars, or other local bodies. This would tell us a lot of things:
1) The odds of life forming are pretty good
2) Life on other planets is noticeably (similar/different)
3) There (is/is not) evidence of life starting on a comet

Yes, because we've got to know things
Let's go through a few questions:
1) Where does the sun get its energy?
2) What is underneath the Earth's surface?
3) How exactly do children inherit traits from their parents?
These questions would baffle Einstein [for most of his life, at least], now it's common knowledge. In the 20th century people spent their lives working on "impractical science stuff", and as a result we don't live in a world of darkness.

In conclusion...
It is a matter of human intellect whether we explore space. When Kennedy promised to send a man to the moon, many scientists were certain that the Moon was covered in several feet of powdery dust, which would make that landing impossible. Imagine that - the moon that humanity has looked at and worshiped and contemplated for millenia - barely known 45 years ago.

We have no idea whether the Phoenix and the Mars Rovers will one day be joined by human travelers, and we have no idea whether those people would come in the name of one country, the world, or Mars Missions Incorporated. But if it's ever going to happen, we have to try.