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Your last edit has the sparkle in the highlights and hints of detail in the shadows the first you post was missing.
While I don't often use Levels for adjusting photos except when doing C&C I use it all the time diagnostic tool early in the workflow when editing to pre-visualize final results. For example with history states on in CS5 I'll adjust a RAW file to where I think it needs to be in terms of tonal range and contrast, open it in CS5 in 16-bit ProPhoto RGB, Resample to 600 x 900, sharpen, then convert to sRGB JPG. Then I open in levels, check for clipping in any channels, and move the middle slider back a forth to see how shifting the midtones affect appearance. It's not unusual to find some things which looked and measured OK in the RAW editor and 100% 16-bit ProPhoto clipping in the JPG.
Skin that is optimally exposed in the RAW will usually be clipping in red somewhere in the JPG. Moving the highlight and shadow sliders while holding Alt/Opt will force clipping. As caucasian skin is pushed to clip in Levels it will clip in red first, then red+green, the finally all three colors. From doing this as SOP if I see red start to clip before the highlight slider is pushed down to 245-240 it tells me the skin is slightly overexposed. If light gray objects I want neutral don't clip at the same time in all channels I tells me there's a color cast my eyes didn't see because they adapted.
Evaluating content like the green tomatoes is a bit tricker. You'd expect a green object to clip in green first, but here's what I saw when I adjusted the highlights to 216 in your image...
To interpret what you are looking at:
white = clipping in R+G+B
cyan = clipping in G+B
blue = clipping in B
What does that tell us? The lighting had a blue bias. Is that a good thing? The way I decide to adjust or not is by comparison. Below I duped the adjusted image then applied a warming filter to the new layer using a diagonal mask to show before (left) and after (right) with a 128,128,128 neutral line between...
Then by moving the opacity slider on the warmed layer from 0% to 100% I can compare various amounts. Greens wreck havoc on perception of color making decisions difficult except by comparison of two variations because that's the color the rods are sensitive to and they are 3000x more sensitive than the y-b, g-m sensing cone cells.
Would I change the color from the original blue bias if it were my photo? Probably not since the actual light was perceptually cool and if printed and displayed in a tungsten environment the ambient light will warm it up a bit. But at least I have a better idea what is actually there vs. what my brain tells me after it adapts my color perception.
Again this is just in the "worst case" analysis phase on a file typical at the end of my workflow. Once I identify all the problems in the JPG I scrap the .PSD file then go back to the RAW and correct the problems in the RAW editor. For example now aware of the blue cast it is an easy fix in RAW with the temperature slider. If I've seen too much clipping in highlights or too little detail in the shadows I'll use recover and blacks/fill. Where the middle slider in Levels just shifts the mid tones, in ACR you can use Contrast to shift the tones then Brightness to adjust the amplitude of the histogram bars.
Usually after making these adjustments for the "worst case" reproduction (small JPG) the RAW image, by normal standards look less than optimal. I've used this same "Kentucky Windage" in workflows when shooting halftones, setting up scanners, etc. over the years so I never considered not doing it with digital photographs. I don't try for optimal at capture: I underexpose the shadows, and if using flash overexpose (i.e. over-fill) the shadows. By normal standards my SOOC files look "flat" tonally because the highlights are dull and shadows are gray, but at the final step when I make the JPGs the tonal range and contrast are perfect.
That's why the towel thing works for me. Keeping whites 1/3 - 2/3 stop under clipping warning winds and shadows overfilled by at least 1/3 stop (when possible) in the RAW being the right amount of "windage" for at the end of the workflow when I make the JPG. That translates into needed to make fewer PP adjustments.