Good work. These are definitely of usable quality, but as an honest critique, they could use some more detail. There’s no shortcut- just lots of tedious hand-painting in of tiny details, going over and over the same spots and adding more definition. But really, good job.
I’m not speaking as an expert or anything- I’ve only dabbled in hand-painting textures, and man, is it tedious. It usually takes me 7-10 hours to get a good result for a single texture, and even then the results pale in comparison to the stuff the experts can make. I guess speed increases with experience, so the only thing to do is keep working at it (ditching my mouse and buying a tablet would probably help as well ;)). I really love the look of hand-painted textures, so it’s worth the time investment for me.
Oh, and I lied. There actually are a couple of shortcuts for adding detail, but the trick is to not overdo them. One trick I use is to paint detailed but small splats or decals with an alpha channel, that I can rotate and copy/paste over the texture to quickly add detail without sacrificing the hand-painted look. Another trick I use is to quickly scribble in random dots and lines with a small, hard brush to add detail, and then blend them in using the smudge brush. But like I said, don’t overdo these tricks, or it’ll show in the end result.