Some scientists who studied the Hadza think that Grandmothers may have made our widening exploration of the world possible:
Perhaps its advantageous when a woman goes through menopause she can now focus her considerable talents & energy on caring for / contributing to the tribe more instead of on only one child(ren). I know my grandmother raised a great family of kids then went on to care for and guide everyone (extended family) for almost 40 years, she shared her knowledge, patience and wisdom, much of which was garnered through raising her kids.
If you are interested in this, I suggest you read Wenda Trevathan's Ancient Bodies, Modern Lives: How Evolution has Shaped Women's Health. There is an entire chapter on the evolutionary advantages of menopause. Definitely check it out.
i think the evolutionary advantage is that the eggs become less viable as a woman ages, and menopause is nature's way of easing a woman off of her menses--and the hormones that go along with fertility--so that she can no longer have babies with those potentially compromised eggs.
menopause is just a symptom of the underlying hormonal changes.
Yes, I can't think of any evolved traits that aren't advantageous, at least for humans living in their evolutionary niche.
The best known explanation is the grandmother hypothesis, which you seem to have found out yourself.
There is no evolutionary advantage to menopause.
Evolutionary advantages are advantages that allow a species to live to the age of reproduction, and increase the likelihood of that organism reproducing. Those species with the advantages consequently reproduce more than those without.
Biological traits that occur beyond reproduction age cannot be affected by evolution. This is why we haven't evolved to withstand heart disease, dementia and other age related diseases.
Menopause cannot increase the likelihood of an organism reproducing, and therefore is not the result of an evolutionary advantage. Prolonging menopause does have an evolutionary advantage, and I suspect that the age of menopause consequently has been increasing over time.
edit: There may be advantages to early menopause, but these benefits don't increase the chances of passing then down to off-spring because the benefits occur after reproduction age. Therefore these benefits don't contribute to the evolution of the species.