A small theory from my side concerning the spirit/aura thing..
As can be seen in chapter 503, Reileigh releases his spirit/aura and knocks out all the cannonfodder. In my opinion this is done randomly, affecting everyone in a certain range. Apparently it didn't affect the Strawhats, nor the two supernovas and their crew. As Joz mentions, a certain level of determination is needed to hold up your consciousness (http://www.onemanga.com/One_Piece/434/04/)
If you ask me this places the Strawhats and supernovas above a number of crewmembers of Whitebeard that were knocked out by the spirit of Shanks. Shanks mentioned he only made 'a bit of a threat' (http://www.onemanga.com/One_Piece/434/06-07/), which if you ask me, could be compared to the spirit release of Reileigh.
Another thing that interests me is yet another thing Joz says in the same chapter. He mentiones that Shanks has amazing vigor and drive, what explains the spirit/aura.
(Definition of Vigor: Active strength or force of body or mind; capacity for exertion, physically, intellectually, or morally; force; energy.)
Something I would like to know is how this spirit/aura is expressed. Do they have it 'on' all the time, or do they suppress it and release it when necessary. And how come that a rather weak person like Usopp is not going down when Reileigh 'releases' his spirit/aura? Is it because he got used to the spirit/aura of Luffy/Zoro/Sanji? Or does he also have the necessary determination to keep standing?