Great points, Shanta. I couldn't agree more, and I would actually go a little further. It turns out that the returns to internal, seasonal migration (moves from village to city within a developing country) are also very large. See here: http://faculty.som.yale.edu/mushfiqmobarak/migration.pdf, and shorter policy briefs on this linked here: http://faculty.som.yale.edu/mushfiqmobarak/monga.htm. And from some circles I get the same reaction to this as what you write above: "Migrants cause problems in cities", "we should focus on growing rural areas". Imagine a policy in the U.S. where the goal was "let's put people back in rural areas." That would take us back 200 years.
I think Kathleen Beegle at the World Bank and coauthors have similar numbers on high returns to seasonal migration in Tanzania. And Ana Maria Mayda (Georgetown?) and Dani Rodrik have done empirical research on the question you end with - "how do people feel about migration?"