Mostly, I would just make the “dark metal” surfaces lighter, partly so that you won’t have problems with “it looks like there are holes in the thing” when it comes time to print the cover.
In the cover shot, the levels of brightness throughout the frame – including both the spaceship and the stars – fall within a narrow tonal range. (Except for the understandably-shadowed areas on her starboard side.) Even where a shadow is being cast by her spine, the depths of the shadow are still comparatively light and therefore discernible.
You might also wish to lighten the red areas a little if you intend to comp this with a starry background similar to the one used on the cover. I would definitely suggest making such a comp for the purposes of fine-tuning the presentation.
Aside from maybe losing that communications-dish starboard-aft (which looks rather like a gray balloon and which seems quite improbable sitting so close to a gun emplacement), the geometry looks suitably menacing.
(Well, make sure that all of the gray thingies don’t look “glued on.” The outside of a space-battleship seems like an improbable place for any sort of “exposed piping,” anyway … any fool would simply aim at them and shoot them off.)