Initially, I was going to recommend continuing the glowing vector style of Defcon one, but we've got a team of artists who could do so much more than that.
I want to approach JohnN to see if he would be interested in the concept art (ships and everything mechanical) for this. Creatively wise, he's more than capable of it (his style is very retro, sleek, and streamlined, however I'd prefer things a bit more chunkier and modern for this).
I was going to oversee the art direction to keep it coherent, and there are many and many space games to draw inspiration from. I'd recommend Eve Online as a big inspiration since it really is the most beautiful looking space game out there in terms of ship designs, the UI, and the vistas that you fly around in. I'd personally tone down the nebulas a bit though.
... personally, I think Sins of the Solar Empire has much better looking space scenes. Darker and just more appealing (although they do have a variety of space scenes with bright reds etc). Do a search for more screenshots as it looks great.
Other inspirations are Homeworld 1 and 2 (some awesome, awesome designs in there - do a search for the concept art for some of the ship designs, great stuff)
(This is linked off Doolwind's blog ;))