I still think Nami's back story hasn't ended. I might agree that she is not someone special (right now). I mean, we all know, by the end of the story, each one of them will be known throughout the world. Now, let's discuss a little bit about the ancient weapons.
1. Pluton
The name itself is derived from the God of underworld, Pluto. We know that it's a deadly battle ship. So, we can say that it basically brings death. Anyone who will sail the ship can bring death at his/her will. Maybe, Blackbeard will be the one to sail it or World Govt has already have it in their possesion. Maybe Pluton could be the reason that it's owners were able to form the govt 800 years ago
2. Poseidon
Clearly the name refers to the God of sea. And Shirahoshi is the one. No discussion needed here.
3. Uranus
This name refers to the God of Sky. Maybe this weapon could provide its user to control the weather and grant it's user the ability to travel anywhere (without a logpose) , maybe the moon and beyond.Now it might sound like a bit of fanfic, but please bear with me. What if Nami's ancestor were from moon or beyond, and they brought Uranus with them. Maybe it is only their lineage who could use the weapon, so the world govt eradicated Nami's parent by attacking the island, making it look like a pirate attack and marine saving it. But, before dying, Nami's parent hid Nami somewhere and Nojiko found her. We know that Nami has a wacky sense for climate (Strongworld is a great example, which was written by Oda himself). She lived at weatheria for 2 years, where she could have learned legends about Uranus, however treated them just as stories (because she is not Robin) . Also if Uranus could help the user to travel anywhere, then wouldn't it will be a great tool for Nami to make maps, even of sky islands, moon and beyond it.