I like the look of the ships.
I have a vague plan to create some steam-punk-joystick setup one day... I always wondered which game might fit that kind of look - and your ships would fit fine! So if you should decide one day to make a full game out of it, I might be interested :-)

If you are looking for some feedback:

1. The used, weathered look of the surfaces is good. If you want to improve that: think where you might want to concentrate grunge, sot, dirt and wear. Perhaps the exhaust or engine is dark from it's own fumes, perhaps the gun-barral is discolored, perhaps there are a few hits by meteors or missiles vissible on the surface.
2. The windows give a great sense of scale on the bigger ships. 3. Consider rendering an Occlusion map in your 3D-program, and bake it onto your existing textures.
4. putting one or two sound-sources on specific (!) locations of your big ships would add a lot of athmosphere. Imagine hearing a dark rumble getting louder when you get near the engines!
5. The thing with the purple "wings"? That is great stuff!
6. I like the fact that there are "themed" design-elements connecting different ships
7. Many of your big ships have places where a small flyer could fly "through". Maybe encurage that (by making those a shortcut, by making them easy to navigate at typical "fighter"-speeds, ect.
8. You have a certain cylinder- or mill-stone-shaped design element on many ships. Consider animating that - perhaps simply by a shader instead of animating it with a script or within your 3d-tool. Same goes for those great purple wings!
9. Can we get a big ship with purple sails? That would be soooo coool!

These models are fantastic, well done!