From what I understand, the Istari were sent in to help the peoples of Middle-earth get through the third age. Why then, did Gandalf help the Dwarves along (and get Bilbo involved) in their quest to rob Smaug?

It doesn't seem to have any use, and I don't remember him having shown any sign of precognition that support a theory relating to knowledge of the finding of the ring or the death of Smaug.