Hi edu, nice to have someone working on map assets!
A few things: You seem to be wasting a lot of space on the UV map (not sure if that's the correct term). If you reorganize it you could have higher resolution textures. Also your specmap is very bright and seems to have nothing to do with the geometry/normalmap or the diffusemap. The resolution of your UV maps themselves should be higher (if they are as big as in the attachment). 512x512 is a minimum but I'd propose you paint a 1024x1024 map and scale it down later if necessary.