Spice, in this context, is an umbrella term for trade goods that were rare, compact, light, transportable, marketable, and more or less imperishable. Even diamonds counted. Spices were generally things people wanted, not things people needed. They indulged the human urge for pleasure, luxury, recreation, ecstasy, and orgasm. Spices, in this larger sense, were a dominant factor in the global economy thousands of years ago and they still are today. (Think drug trade.)
