The way I see it...
Gol D roger was a helluva smart bastard and as such he could easily foresee that if he publicly announced that his goods were up for grabs all the greedy bastards will go out to sea even in spite of the World Government; he'd enjoy the joke if he knew that his words got as big as creating a new pirate era.
But he wouldn't have been 'the' greatest pirate of all time if he did not really collect any real wealth, and not just treasure in gold and jewels (though that's an essential part of it
)
My best guess is something that could be the end of WG and give back the people their freedom (we already know that the final Poneglyph of true history is on Raftel, and there might be more).
(There have been speculations about the people before the WG's age and if the Ds are descendants of theirs, in which case the Ds would be taking back what's rightfully theirs. Could be. And the remains of that civilization might be collected on Raftel.)
And let's not forget that the Strawhats not only follow in Roger's footsteps, they aim to become his successors. At the moment they are behind his achievements but it's inavitable by the climax that they surpass him. For example it seems clear to me that they will have to end the WG's rule (Dragon's already aiming for that for godssake, and Luffy cannot aim any lower than him) in fact that might be the final of the story.
And just an idea: Maybe there will come a point where they are in possession of Roger's heritage and can take over where he left off. The crew might insist that they take this chance (especially if the "heritage" is some powerful knowledge or weapon)...and Luffy would probably answer "Nah, I respect Gold Roger a lot, but I'd rather do things MY way."
