"does everyone need the dividend?"
-No. No one NEEDS the dividend, but it becomes a question of equity and parity to say "Due to these criteria, you get the money and you don't."
"are there more efficient ways to help lower-income Alaskans than paying the same fixed amount to everyone?"
-(Arguably) yes. How about this - anyone who receives public funds (food stamps, subsidized housing, etc.) Does NOT get a dividend (as they are already receiving a level of public funding above the median/standard/norm) and the dividend is only given to those who have not received public assistance in the last 24 months. Not fair? Exactly, and neither is giving a means test to the dividend - either everyone gets it or no one.