Quote (i_r_slayer @ Dec 4 2010 04:30pm)
Obviously they set their log to another island and caught another route.
Skypiea was an awesome arc.
Introduces a form of haki.
Klabautermann
Robin learns about an ancient weapon and is encouraged by Gol D. Roger to continue searching for the true history - Probably the most important thing that happens, if it weren't for this I think Robin may not have continued
Zoro learns the 36/72/108 pound cannon
Chopper "Becomes a pirate"
Usopp Uses dials to upgrade his and Nami's weapons.
The ship receives a lot of damage and the crew receives a lot of gold - Leading to great things like Usopp leaving the crew and Franky/Sunny.
To me the sky island arc most embodied the concept of adventure. Learning that Roger had spent time up in Sky Island was also extremely interesting.
Not only did it introduce a form of haki, but Luffy learned a method of combating it. Random attacks as opposed to calculated, planned ones.
To add to your list, they also got Nami's beloved wave runner :]
But the main and strongest point you made, without sky island there would be no robin, franky, or Sunny. Not only this, they might not have gone to Water 7 so the whole CP9 thing might not of happened. The other paths he could have taken may have been supremely less epic in the long run. Oh, and Luffy & the others ended up saving many thousands of lives from Enel's tom foolery up in Sky Island.
By far one of my favorite arcs.