Yeah, loggie taught me when your done making your sig, merge your layer, sharpen it up over once, and than put it on low opacity, or just sharpen with low strength.
Just make a new layer, and sharpen or smart sharpen(for ps users), that way you can pick how strong the sharpening is. But at the sametime you need to make sure you don't over sharpen and sharpen the text too much.
At the sametime, since you use gimp, make a new layer and apply image, sharpen on like 10 then get out the sharpen tool(soft brush) and sharpen certain spots, maybe even slightly blur some spots to make the render pop more.