The problem with using legacy items is that if you ever wanted to implement those items... well you end up with the same problem as if you were implementing the city of Besaid somehow. Possibly even more so than with the city problem. Same applies to Monsters, certain artifacts etc.

Characters gets around this problem, as it would not be right to introduce a character fundamental to another FF game (some exceptions, such as Gilgamesh or the Dissidia situation). If you wanted to get really fancy, you could name them after auxillery/non-core game characters such as Marche or Layle.