Well, I just got through doing all of the event (unless theres something else, not involving the Treant). Basically, to get the robe, you need to have brought a decent amount of Joy to Vana'diel, and do one of the runs a 2nd time, in any of the cities (you don't have to do all the cities 1st...just go and do 1 city twice, but make sure you've given enough Joy through presents and fireworks).
For the +1 robe, you have to do a 2nd city twice (again, do not need all 3 cities done 1st), and...you'll either get the +1 robe, or fireworks. Make sure you have room though, I got screwed out of my 1st HQ robe the 1st time, because of my inventory being full. Also, the +1 robe "Enhances the effect of Selbina Milk", so it should be great for low level jobs.
As far as I can tell, theres nothing special for doing all the cities twice, so I wouldn't bother wasting your time doing it, until somebody shows proof saying otherwise.
For the +1 robe, you have to do a 2nd city twice (again, do not need all 3 cities done 1st), and...you'll either get the +1 robe, or fireworks. Make sure you have room though, I got screwed out of my 1st HQ robe the 1st time, because of my inventory being full. Also, the +1 robe "Enhances the effect of Selbina Milk", so it should be great for low level jobs.
As far as I can tell, theres nothing special for doing all the cities twice, so I wouldn't bother wasting your time doing it, until somebody shows proof saying otherwise.