"By convention sweet, by convention bitter, by convention hot, by convention
cold, by convention color: but in reality atoms and void." - Democritus
What is anything really worth? By convention, sweet is sweet. Things are worth what people agree they are worth. That is the market. Anything is worth what people will pay for it.
What about the air? It is worth a lot, perhaps worth everything, yet it is free. What about water? What about life?
What is money really worth? Is it worth the gold it contains or represents? Is it worth the labor it represents? Is it worth what it can buy?
What is gold really worth? If you really want to know, check out BullionVault's Italian site! It is just a metal dug up from the ground.
Which brings us back to Democritus. By convention, gold, money, things have value. That is the market.