what is the point in putting effort in to the concert minigame?
Converse with fellow players
If you don't do the minigame/do it poorly, during certain parts of the concert where it zooms in on your character, your character will stumble, and everyone around you gets to see you stumble and secretly laugh at your lack of dance skills.
That's about it. Though, there's not really a point to joining the concert either aside from getting to dance (you just need to be in the shopping/gate area to get the buff), so you may as well look good while doing it.
I was wondering bout the same thing myself, nice to know that the dance mini-game is totally optional.
(Even doing the mini-game well, it looks funny when a male CAST is doing them, I think most of the dances were meant for female characters)