I don't think there'd be anything interesting in David's past...all we need to know is that he drowned, he played football, never got sick -yawn- had a car accident (which we did see in the original btw), got married, had a kid, etc. nothing really exciting. It would be more interesting to see more of elijah's past, though. Maybe he came accross more people he thought might be "special", his attacks, maybe he came accross other comic book experts, i dunno.