A theft of this nature would require a lot of long-term planning.
And resources!
And that is where this whole 'gold heist' theory falls down. If you have the resources to steal an aircraft full of gold/diamonds/Justin Bieber CDs, fly it anonymously to a secure landing site and off-load the booty, then you may as well just hijack the truck on its way too or from the airport!
Much cheaper, less risky and involves a hell of a lot less people.