You'd be hard-pressed to top Dan O'Herlihy's Grig and Robert Preston's Centauri. You really need a fast-talking door-to-door salesman for Centauri's role, and Grig...face it, you need a REALLY good actor to emote through the mask like he did.
Besides, who plays coinops anymore?
In all honesty I would like to see it - I thought, overall, the "war" was pretty short and one-sided, but it worked for the story. And the Gunstar is an absolute classic of design and arguably one of the most believable/realistic SF ships out there. I really hope they keep her aesthetic and design.
Castwise...oh, let's see. Your lead's gonna have to be someone young, post-highschool pre-college, couldn't say anything from that pool. I will say pick an actress for the lead simply because I'm an anime fan and cute girls in spaceships is awesome. For Centauri, how about John deLancie? He'd really play up the put-upon parts of the role, and I think he can be quite convincing about doing something if he really wants. Not like he's a stranger to the big screen either. Grig...could go lots of ways, but you need someone good at emoting through heavy makeup. Ian McDiarmid? It'd be fun to see him as a good guy for once.