I don't have an example handy of using the technique I mentioned above for creating highlights, but here's an example of doing the reverse - selectively adding saturation using a Multiply layer.

The top image is the original washed-out photo. In the bottom image I first adjusted the color balance, then created four copies of the background layer, set their blending mode to Multiply, merged them all together and added a layer mask. Then I airbrushed the mask to add saturation to areas of her face.

Admittedly this is not a great example! The original is badly washed out and you can't enhance something that is not there.

Gromit