Even countries that are relatively open to (legal) immigration, like Canada and Australia, tend to limit immigration to working-age adults qualified to work in technical, professional or otherwise white-collar jobs. So I think it's fair to say that you do increase per-capita income.
I wouldn't put the US in the same boat as Japan, though. Between green cards and naturalizations, the US receives well over 1 million immigrants per year (that doesn't count non-immigrant visas like H1B etc):
Even countries that are relatively open to (legal) immigration, like Canada and Australia, tend to limit immigration to working-age adults qualified to work in technical, professional or otherwise white-collar jobs. So I think it's fair to say that you do increase per-capita income.
I wouldn't put the US in the same boat as Japan, though. Between green cards and naturalizations, the US receives well over 1 million immigrants per year (that doesn't count non-immigrant visas like H1B etc):
http://www.voanews.com/content/us-issues-million-green-cards...