So the shadows would still darken them anyway. The trick to the above is that after doing the level shadows and the texture shadows, which are all pure black, you render a quad over the scene set to add blend with the ambient light color. That brings them up from pure black, and you now have shadows which blend together nicely but aren't pure black in the final scene.
This would be the method I'd naturally opt for if I couldn't get a nice blend from a straightforward render. Trouble is I use an overlayed quad for reflections - if you start to stack too many effects this way then you just end up render(shadows)...render(reflections)...render(bloom)...render(final scene) and you can only show a (really nice looking) cube before the framerate nose-dives :D