I'm not so much talking about style as I am technique. Obviously, if you shoot landscapes you're stuck with what light mother nature gives you. The option of pulling shadow detail is great under certain circumstances, but if you have the ability to manipulate the quantity or quality of light, you'll do it every single time instead of cranking up on the shadows slider. Whether you're using something as simple as reflectors or off-camera flash, or something a bit more advanced like monolights, 30-foot softboxes, or gazillion yard long muslins to diffuse natural light, the quality of light often takes precedence over the quantity of light. Why else would high-end commercial photogs - one of the few remaining groups of photogs that are actually wealthy - bother with monolights, 30-foot softboxes, and gazillion yard long muslins?
I take a lot of portraits/indoor shots. I have been focussing on quality of light as I found the standard umbrellas to be too harsh - my light sources have to be transportable as I go to the subject rather than use a studio.
Possibly my biggest single improvement recently was the move to 7 foot parabola umbrellas coupled with the use of 1/4 cto stophen on the main shoot through light. At about £100/c. 150usd each (I have 3) the quality of light significantly improved for less the cost of a decent lens.
I find that DR (as shown in the DPP histogram) of 8 or more seems to give top IQ - this is about 2/3 of the histogram on the camera. I have found that good quality light plus good exposure means you dont have to push the shadows.
I always have a flash in the bag to help me out with the dark areas in strong sunlight - this is the way we did it with film - and the technique works for digital too - remember those wonderful hammerhead Vivitars? Contra jour was handled with a small (36 inch) reflector to get light onto the face
Clearly there will always be occasions when you have to push the exposure - but good technique will get that down to the very rare exception for the majority of shooters. If this is true for a puchaser of either the 5D3/D800 then the shadow performance will become less important than the other features.