If I get an underexposed shot, what I do is increase the exposure to get the midtones correct and then pull down shadows and highlights, that way the shadows become brighter but with no more noise. Normally though, I ETTR and I say out of the 50k shots with the 1dx so far, I have pushed the shadow up no more than 6-7 pictures. Pulling them down, however, I do frequently.
The CPL is a very good point, I use it always outdoor, and it REALLY adds to the image, clearly DR, but the overall punch is so much better. Many people underestimate the power of a CPL.