In Lightroom 4, when editing a RAW file, what's the difference (if any) between the following edits:
A). +30 Contrast
B). -30 Highlights, +30 Shadows.
Do these do the same thing?
Well, as they say, a picture is worth a thousand words. The GIF animation below shows +30 Contrast, +30 Highlights/-30 Shadows, -30 Highlights/-30 Shadows:
The differences between the three are subtle, however there are indeed differences. Contrast increases the spread of tones across the tonal range, so technically speaking, +30 Contrast is more like +30 highlights/-30 Shadows than it is like -30 Highlights/+30 Shadows. However it is dissimilar from both, in that adjusting contrast also affects color saturation as well as tonal range. This improvement to color contrast is evident between the first two frames of the GIF animation...the colors are more washed out in the +30H/-30S frame (most readily visible in the fence.) Adjustments to contrast are also more likely to affect the entire dynamic range (every tone in the image), where as highlight and shadow adjustments are purposely designed to affect a restricted range of tones.
It's definitely not (and your -/+ signs on the B part are reversed). Here's an example of +60 contrast and +60 highlights and -60 shadows:
Adding -30 blacks and +30 whites helps, but isn't quite there (notice the grass mainly):
Overall, its difficult to replicate the effects of the contrast slider exactly by manipulating individual sliders - but you can get close. Most notably is the difference in color contrast.