The Danger with Using Old MUsic
The reason for re-using the old soundtrack = help audience recall the good feelings of youth through the songs they like and connect it to this movie..
For that to work, the current movie has to be at a minimum level of quality.
The danger in this case is, instead of the audience falling in love with the current movie, they associate the crapness of it with the soundtrack and can no longer enjoy the songs!
:(