I think dear Bart plays a pretty signifigant role in this story.. but it has nothing to do with him dying or ever getting hurt.
How-ever, what Bart shows, is how the strawhats status has changed.
When we began the manga, they were a bunch of nobodies, nobody had heard of Strawhat Luffy or the straw hat pirates, they were loosers. Luffy would say. "I'm gonna be pirate king!" and people would go. "riiiiiight." in a very unimpressed manner. He could introduce himself. "I'm strawhat luffy!" and most people would go. "Who???" in the beginning of the manga that is.
How-ever... now Luffy and the gang is infamouse, they have enemies out for them they havn't even met, they have stories told about them across the world and they also have... devoted fans within the univers.
And Barto is a symbol of their progression, he is a huge fan boy, but not just a looser, a strong well accomplished pirate himself whom made a name for himself, and yet still looks up to the straw hats as his heroes.
He never met them personally, never talked to them personally, unlike Coby or Vivi never had a personal adventure with them that changed his world view.
He only saw them from afar, and still they inspired him to do some-thing great himself.
That he knows of all the things they did, shows how far the stories about them have actually spread.
That shows how signifigant the straw hat crew now is in this world, and just how huge their influence is, they are now influencing things they have never heard of, influencing things they never have been any-where near, they just are.. that big, like a big bunch of rock stars with a fan base they have no control over.
Barto is a pretty signifigant character in show casing this, how large the myth of the straw hats has grown also... talking about self insersation, he kind of also represent all the real life fans out there that would act pretty much the same way if we ever got transported into the manga, doesn't he?
It's perfect!
