Way too much noise/scratches in your diffuse, put most of them in the spec only. You should multiply your AO over your spec aswell. Like has been said already you have to fix some of those normal map errors, they make everything look really messy.
Yeah, i think before think too much about shaders, you need to improve that texture. Also keep in mind that a shader isn't an afterthought. All shaders can be a little different, and you should create your texture content specifically for your given shader. This means previewing your work in the shader while you're…