Great topic, Wes!
Here are some aspects of the topic that Chris Burk, our Debate Expert, thinks will be debated. What does everyone else think?
Overview effect -- astronauts and other visitors to space look at the earth & their worldview changes. they want to do more to preserve the earth's environment.
Astronomy education - looking at the stars from earth and learning the earth's place in the universe does the something similar
Mission to the Moon
Mission to Venus - learn about greenhouse effect and apply that knowledge to earth's environment
Mission to Mars
Mission to study the Sun - everything from solar variations (which affect our temperatures here), solar flares, solar storms, and more. Solar radiation affects our satellites, electrical grid, radios, etc.
Mission to _____ - any planet in the solar system might be worth a mission since we might learn something
Asteroids - two major issues here, Asteroid mapping and asteroid mining.
SETI - Search for Extra-Terrestrial Intelligence. Maybe little green men from Mars. Or maybe we could just simply listen for communications from other civilizations.
Deep Space probes
Exploration in cooperation with X country - Prime candidates would be Russia, China, Japan, European Union, India, and maybe Israel. The focus on such debates would not be the space project per se, but the increased cooperation with an important country. The benefits might be economic (boost the Russian economy, for example) or political.
Manned or unmanned missions - Many who write about space believe strongly that putting humans on the missions is stupid and costly. There's no reason to send actual humans to Mars, for example. The rovers are better and less costly and less dangerous without actual astronauts. However, a vocal faction also believe that staffed missions raise the profile of space exploration overall and capture the public's attention. That's necessary secure the political support for the overall space exploration mission.
Private companies and enterprise in Space
Prestige - Successful space missions build a country's prestige. That's what the space race between the USA and the USSR was all about.