Seems like the effect of this cannot be seen just by targeting the nodes, it'll only be visible once you begin the gathering, conditions and effects can be seen in the "Location Effect" part of at the buttom of the gathering window.
Which nodes have an affect seems to be random, among the ones without a predetermined effect, the effect seems to stay if you cancel the gathering, but things that changes nodes seems to be able to remove it, like gathering other nodes, or leaving the area.
The required stats are identical to the requirements of the other bonuses of the same type in the same cluster, so if +5% Gathering Fortune requires 444 perception, +30% Gathering Fortune will also require 444 perception.
I've noticed the effects of +30% Gathering Fortune, +2 Gathering Attempts, and +1 gathering yield.