What strategic value does the treasure hoard of Erebor have that makes it so desirable for so many factions?

What strategic value does the treasure hoard of Erebor have that makes it so desirable for so many factions? Will the gold be used for trade and industry by the parties involved? Is it merely greed or a symbol of power? Are there magical items hidden within the hoard?

I understand that of the Five Armies, the Men of Laketown will benefit from the wealth of gold, as they can use it for trade to rebuild their city. But what of the Elf-King? Do the gems (white gems of pure starlight in the Peter Jackson films and green emeralds in the books) really possess such value (such that Mirkwood needs) that they were worthy of mounting a military campaign? And what of the goblins? What need do they have of gold and treasure? I doubt someone will engage in trade with them, besides, they're more of a pillaging folk, aren't they?