IMO that little bolt is pretty useless; I just adjust it once so the brake looks nicest, and centre the caliper by hand. Star washers between the caliper and frame are pointless too IMO; they only damage the paint. The mounting nut doesn't need to be super-tight; I've always done it up tight enough for the brake to stay put, and loose enough to manually centre the brake, and I've never had a problem.

Also, with a dual-pivot, perfectly centred isn't perfectly centred: if you have the same gap between pad and rim on each side, you'll find one side hits the rim first, pushing it to one side, and you can feel this through the lever. I centre the brakes by ensuring both pads hit the rim at the same time.

DPs are easily centred by hand; I've found the best method is with your thumbs under the pads and a couple of fingers of each hand resting on top near the mounting bolt. Pull the brake open with your thumbs, biasing to the direction you want to move it.