Answer:
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.
Double my number, I'm less than a score. Half of my number is less than four. Add one to my double when bakers are near. Days of the week are still greater, I fear.
Each of these ends in a kettle full of precious metal and the double variety is quite awesome
Steals an event or even a mood. Reveals the truth or shatters it.
To cross the water I'm the way, for water I'm above. I touch it not and, truth to say, I neither swim nor move.
Of these things - I have two. One for me - and one for you. And when you ask about the price, I simply smile and nod twice.