I always assumed (and played with it as a kid as such) that the rotating body around the cockpit had to do with creating a larger firing circumference. Which would equate to more damage or chance of damage to the enemy. Sort of a "spiral death blossom" effect.
It'd make sense if the ship spun around the cockpit rather than the cockpit spinning on its rotor and the ship remaining completely still relative to its engines. The only purpose of a cockpit rotor is to jam at maximum at the worst possible time.
Also I never thought of something as I read a few replies above in there not really being a reason to build a Deathstar when you already have things moving at, or in the case of the Falcon's boasted .5 past, light speed. Imagine a Star Destroyer, of which the Empire has more than a few, smashing into a planet at light speed. I assume that might be akin to the doomsday asteroid theory no? Destroying a planet's surface to some degree but leaving in possibly intact to be terra formed or used as a natural resource.
The nature of hyperspace is such that it stops working if you drift too close to a mass shadow, hence Interdictors. That's why you can't hyperdrive into a planet. You can hyperdrive so close to a planet/star/black hole that you have severe issues not hitting it, but you won't hit it at lightspeed.
Not that the EU doesn't ignore that detail from time to time.
Edited by TIE Pilot