Another method would be to use ambient occlusion or cavity map to control dark areas, by multiplying them over the spec map. In Photoshop/GIMP you could try to take the black-and-white version of baked diffuse texture and play with 'levels' or 's-curve' and bring the very bright areas visible.
This is quite different approach than in hard surface, where we play with strong edges rather than baked shadows. To make a specular map (again, according to my opinion), we should make the specular effect very strong in bright areas as almost black in shadow areas. Just as in Fernanda's baked texture example above. When we model clothes in SL, the shadows/ambient occlusion are usually baked inside a diffuse texture. On the other hand shadow areas do not have any specular at all. We see that specular effect is mostly visible where light falls on the surface and reflects back. Let's look at a real world example of a leather sofa (image below). That is true with hard surface models, but not necessary true with soft and organic models. By making those areas white, we mimic very bright specular in hard corners. The idea is to use hard edges that are found using normal map and Photshop 'find edges' filter and start to develop specular effects around those areas.
