I use my 1DSMK3 for both kids portraits and nature and wildlife and agree with your sentiments. I really only ever look at the histogram anyway - the viewfinder is so bright its easy to compose the image through the viewfinder, then just check exposure on the histogram.
This is the sort of argument that people use when their camera is lacking, for example, in good high ISO performance. "I never use high ISO, so it's not an issue".... "I never use LiveView, so it's not an issue." Could be, the reason such people don't use such features is because those features on their existing equipment are not all that impressive.
When you look at a LiveView screen at 10x magnification with a 40mm lens, you are actually seeing what you would see through the viewfinder with a 400mm lens (with the limitations of the LCD resolution, of course). If you were to use a 400mm lens at F2.8 where focussing is very critical, LiveView at 10x magnification would give you the close up view you would get with a 4,000mm lens, looking through the viewfinder. That's a closer view than you would get stacking three 2x extenders on that 400mm lens.
However, such impressive magnification is only really
useful if the Live View screen is sufficiently high resolution. I recall a problem recently, when I was comparing the resolution of the 40D and 50D by photographing a banknote (more interesting than a line chart, I thought). Using Live View at 10x, I was sometimes unsure if focussing was really spot on, with the 40D, but never unsure with the 50D. To be certain I was focussed accurately with the 40D (even using LiveView at 10x), I had to resort to the same technique I use when trying to manually focus on line charts when looking through the viewfinder. That is, look for the tell-tale signs of color aliasing which always appear when lines are at a sufficiently close spacing, but only when the focussing is spot on. (Such aliasing is much less obvious, of course, when the light signal has passed through the sensor's AA filter.)
Unfortunately, most scenes in the natural world do not contain closely and evenly spaced lines to aid manual focussing in this manner.
Of course, it goes without saying that such critical focussing is only likely to be necessary when shooting at wide apertures. Even at wide apertures, autofocus can
often be accurate enough.