I also want to to see a bit of the campain in the demo and a Tutorial so i know how to play it. The AOE:III demo did not have one and left people confused.
Well if you do scrap the death star you could be rich. Just think of all the metal that you can sell, Anyway there are some uses for it like an endor style trap.
What everyone else has said. Anyway i have thought of a tactic. You could destroy a plant which is between your planet and an enermy planet thus slowing down there attack times on your planet.