the mp3 could work rather well. the audience could think it is the soundtrack, but in actuality it is what peter is listening to. those kind of reveals can be quite novel when done right.
also, it shows that peter is loving life as spider-man and that he has become somewhat arrogant and cavalier.
this connects with what i've previously speculated; spider-man/peter starts off on top in this film, before crashing back down to reality, so to speak. the parker luck will rear its ugly head early in the 2nd act.
i highly doubt the mp3 will be used once things get serious.
it all could serve to enhance peter's arc in the film.