I think the key is remaining true to the essence of the the characters. Spider-Man could be black, white, Asian, Latino, as long as he's that same working class kid from Queens we’ve come to know and love. (As current Spider-writer Dan Slott once observed: "There's nothing inherently white about Peter Parker.") Superman could be any race (I mean, the guy’s an alien. Why can’t Kryptonians be black?) as long as he embodies the spirit—that magical balance of otherworldy power and simple human decency—that Kal-El has come to stand for.