That might work, but why give them the ability to post stories initially? That way, to get karma they would have to be able to impress the insiders with what they have to bring to the table personally and can't just find some good stuff made by others.

You could even combine them, so that the threshold is different - you can post stories with karma of, say, 30 but you can't vote before you have hit a karma of 500.

I have lived in my country all my life, but I was 18 before they let me vote.