Hmm...As long as an Earthbender is surrounded by Earth, they can take on pretty much anything. Although it is a weakness that they might not always have ample supplies of earth. They can easily protect themselves from any element, and can dominate anyone who doesnt know how to face an earthbender. Toph actually taught Aang how to see through earthbending. You see Aang doing this in The Runaway and in the finale. If Toph can teach this ability, then isnt it also possible for Toph to teach other earthbenders how to metal-bend? Not to mention the other variation, sandbending. When you combine all of this, I'm not really sure a special event is really needed.
As for Airbenders, its extremely hard to defeat them, considering they can just evade pretty much everything, and then corner you and prevent you from bending with intense wind. An airbender can also manipulate small amounts of earth to throw at enemies. An extremely powerful airbender can create wind strong enough to break right through solid rock. Considering that they can fly around, evade, and even manipulate certain other elements, I dont think they really need a special event. Besides, Airbenders arent inclined to fighting, so extreme power isnt really needed.
I can't really think of a special event for an Earthbender, an Earthquake would probably just weaken them. Maybe strong winds might help Airbenders with the intensity of their blasts though.