Another reason I found to repeat this event is: it has been only repeated once, while the Lightning Strikes event has been repeated twice before the items were available in Mog Station. I think that the Shantotto event should be repeated once more to be equal with the Lightning event. This should be also done with the Dragon Quest event (it also was repeated once instead of twice), and with the recent Iroha event (this one still should be repeated twice in the future). So: each collaboration event should be present at least 3 times before Mog Station.