I like the idea. It might actually work if it were turned into some type of Mega-Event where if you don't take a certain planet from, say, the Korath before they finish building the Doomsday device, then everyone in the galaxy will get anhilated or something to that effect...
Nah, on second thought, that's too harsh. It would be more annoying than fun, really. Prolly the same with the Terror Stars too.