How important are these side competitions to you in a game? Do you strive to be the best just as you would the gym battles? Or are they something you ignore as much as you can?
I personally like them all, though with the exception of Black and AS haven't really competed in them as much as I would like. I really felt the incentive in AS to win! You got some really good rewards and neither the Contest or making Pokeblocks were complicated and didn't take too long. I loved seeing all the Ribbons on my Pokemon and the sparkly bow when you send your Pokemon out to battle!
The Musicals were cute but you didn't really have to do much and got a little repetitive with no real great rewards. The Pokeathlon was interesting and fun but I never played it that much. I may go back and explore it some more!
I like having these competitions in the games as a side quest of sorts and hope they'll continue. It would be cool to have Gym Battles, Contests and Pokeathlon all in one game!