Well, you beat me to it. That was going to be my next point.Wait, there's still one asymmetry: time on Earth's clock in Earth frame is longer than time on spaceship clock in spaceship frame. But that creeps in because we say that spaceship(I assume you meant spacestation here) is at rest with respect to earth, so, proper length is 8 ly. If we considered, say, another spaceship at 0.8c, 8 light years behind our spaceship, and considered the time difference between events C and D which are "spaceship one passes earth" and "spaceship two passes earth" respectively, we'd get exactly the reverse results.
But I still say that this asymmetry is present in the "twins paradox". Not the only asymmetry there, but it's still there. My goal was not to "make the situation symmetrical". My goal was to have a scenario like the "twins paradox" without the asymmetry of accelerating vs. non accelerating frames, but still with the asymmetry of having the distance specified by a location at rest with earth.