Could Smaug have destroyed Rivendell?

[The Lady of Ithilien]

In the appendices to The Lord of the Rings there is an account of the meeting of Thorin and Gandalf at the Inn in Bree which says that Gandalf was worried how Sauron might use Smaug "with terrible effect," and he later says to the hobbits that Smaug might have destroyed Rivendell.

That raises some questions.

-- Wouldn't the power of Elrond's ring have prevented that, either directly somehow (it seemed to be associated with water), or perhaps in conjunction with the remaining Noldor in Rivendell, indirectly by "hiding" Rivendell from Smaug, even from the air?

-- Why Rivendell? There was already a conflict in progress, according to Haldir, between Lorien and Dol Guldur: if Sauron could influence the dragon, wouldn't he have already done so against Lorien? Or had Galadriel somehow prevented that because she could see straight through the darkness?

-- What treasures in Rivendell and Lorien of the material kind that dragons crave would there be to draw Smaug away from his golden bed in Erebor, anyway?