And then there is basically no information that backs up exactly how much total mileage will be saved by only charging to 50%. Are you charging to 50% to get an extra 10 miles on a battery that's going to last 300,000 miles?
How much will you shorten your life by smoking 1 cigarette, 2 cigarette, 3 cigarette?
Just because the effect is not perfectly quantified, does not mean the effect is not known - that smoking is detrimental to health. Same way , it's known in Li-Ion battery chemistry that high state of charge is relatively more stressful than mid state of charge (along with temp, current, etc)
What it's worth to each person is a personal matter. I do 80% because it's convenient to me. And I'll puff on a cigarette once in a while, too.