Nothing can look like real metal when it's just a color map, no matter how hard you try. You'd need a specular map and a bump map at the very least, and an ambient occlusion map rendered on top of your color map.
If you're looking to use the textures in a game engine that doesn't support bumps or specs, then what you need is to look into texture baking. It's much easier to get a more realistic look out of your textures when your 3D program does part of the work for you. For example, if your engine doesn't support bump maps or spec maps, you could render some of those effects into your color map... it wouldn't be ideal, but it would not look as bad as if you didn't have these effects at all. The model would have a "pre-lit under fake lighting" look to it, like the original WCP ships do... it's not as bad as a "not lit at all and really plain!" look.
At the very least, even if you don't want to fake the speculars, you would be able to render an ambient occlusion map and add it to your color map, which would already make things look a bit more natural than having plainly-lit textures all over the place.
Sticking to strictly 2D tutorials doesn't help much when you're trying to texture 3D models for use in real time. For example, in the two textures above, the second one looks too bland from not having any lighting but the first one, because it does have a shadow that was made arbitrarily in a 2D app already, will most likely not correspond properly to the lighting in any part of your model. Try combining the first method with "real" 3D shadows (rendered by your 3D app) and you'll have a much better result.
(Google up "render to texture" or "texture baking" - I'm not sure which modeling package you are using but it's pretty much a standard feature for them all).