They do not matter in current era MMO's. There is no new content added for those levels in content updates or expansions. In fact, there is usually stuff taken AWAY form those levels after an expansion or two.

14 forces people into lower level content in roulettes specifically to make sure people doing old content actually have people to do them with. Most every other mmo takes the "just dont bother doing old content unless you have a friend carry you" approach.