For the Orcs it's not about strategic value, it's about good old revenge. As the book says:
So began a battle that none had expected; and it was called the Battle of Five Armies, and it was very terrible. Upon one side were the Goblins and the wild Wolves, and upon the other were Elves and Men and Dwarves. This is how it fell out. Ever since the fall of the Great Goblin of the Misty Mountains the hatred of their race for the dwarves had been rekindled to fury.
The Elves are assigned two motives; one is helping out the Men:
But help came swiftly; for Bard at once had speedy messengers sent up the river to the Forest to ask the aid of the King of the Elves of the Wood, and these messengers had found a host already on the move, although it was then only the third day after the fall of Smaug. The Elvenking had received news from his own messengers and from the birds that loved his folk, and already knew much of what had happened.
And the other is greed:
"That will be the last we shall hear of Thorin Oakenshield, I fear," said the king. "He would have done better to have remained my guest. It is an ill wind, all the same," he added, "that blows no one any good." For he too had not forgotten the legend of the wealth of Thror.
As for magic items in the hoard, sure there are:
Altogether those were good days for us, and the poorest of us had money to spend and to lend, and leisure to make beautiful things just for the fun of it, not to speak of the most marvellous and magical toys, the like of which is not to be found in the world now-a-days. So my grandfather's halls became full of armour and jewels and carvings and cups, and the toy-market of Dale was the wonder of the North.
Undoubtedly that was what brought the dragon.