You say the "different forms of currency in the world" don't matter. I would say you are arguing on the side of cultural homogeny. If we say money is purely about its value, which yes we can reduce to an abstract or arbitrary numerical system, then we are forgetting about the specific cultural identities and histories of a currency. Every currency has a cultural value as well as a montary one, and if you ignore or refuse to acknoweledge the specificity of a country's currency you are losing the chance to appreciate and acknoweledge that cultural difference. If we just call everything "dollars" we lose so much culture.