Some of them just have to be flat and clean. So I think that a detail normal map is an acceptable solution for my problem but not for every model I plan to create. With the highest glossiness of the material I can clearly see the waves coming through the detail normal map.
So I tried to hide these with a detail normal map over the existing one, with tiny scratches, cracks, bumps, which made pretty good results with the right shininess of the material and light settings. But I'm sure with a brighter texture you could clearly see these waves. After your reply I gave up generating new normal maps over and over again and textured my model with a test grid texture from Blender, which made the artifacts less noticeable.
