The sins textures are pretty scalable. Like what was said though make sure your bloom, AA, etc. is turned off. Running at minimum resolution helps too (1024x768). Turning off the colored skybox, dustclouds, planet elevators, deep space backgrounds, and asteroids will help too. Less stuff to render.
If you still chug on low settings, and all that stuff disabled, then you may have a bit of a problem.
How "low end" are we talking about with your machines?
The only way to "nerf" it even further is to remove the main mesh's and replace them with "lod" meshes. They are supposedly in game, but i have yet to confirm it.