I found it really weird that Superman's ideal fantasy world would be a place that had no Lois, no Jimmy, no Ma and Pa, or anyone he met in lifetime on Earth. Yes, would desperately want his home planet back, but to be that dismissive of everyone he ever actually cared for in real life never sat well with me, no matter how well 'For the Man Who has Everything' was written. I'd take the other extreme over that characterization any day of the week.
The biggest problem with the 'Superman as immigrant' idea is that he's a child immigrant. He was brought up in American culture from when he was a toddler at the latest. The closest parallel I can think of is the kindertransport where a lot of Jewish children were brought to England before the Holocaust, many of whom never knew their birth parents were Jewish. I knew a man who didn't know he was adopted or Jewish until he was in his 60s when he came across the adoption papers proving he was in the kinder-transport. He started learning about Judaism as an elderly man. Kara is closer to the 'Ellis Island' experience in that she was actually raised in Kryptonian culture and human culture should be alien to her.