the value of sth waters down, 贬值

I think the value has gotten a little more watered down over the years. If you look back 20 or 30 years, and look up the number of people who had M.B.A.s, there are probably five times as many in 2006. It means comparatively less now than in 1966, because there are more of them. That's why the value is greater at the top schools.