I think that Gollum and Smeagol were two separate persons. The "character" the ring was capable of evoking in such creatures as Galadriel (instead of a dark lord you would have a dark queen) and Gandalf (through me it would wield too great a power) indicate that even they (Elflord and Maia wielder of Narya) would exhibit profound darkness if the ring were given the chance to do so.
If Gandalf and Galadriel are as susceptible to become dark rulers, then it is likely the person of Gollum is a manifestation of the ring itself through the being and person of Smeagol. I think that the degree of cunning and malice exhibited in Gollum shows the character of Sauron.
The construction shows that "into the ring was poured malice" and "will to dominate". Those are attributes of intentionality, and were done with purpose in aiding the ring of rings to achieve for Sauron what he intended.
The one ring is meant to be a ruling ring of rings. The rings were meant to cause leaders of a race to be able to evoke the most characteristic excellences of the races. The "center of elvendom on earth", Lothloriedorinian, came into being as it was in part by the use of the Elven rings. The great dwarven kingdoms likely have similar correlation. The ring was meant to make rings of rulership more rings of rulership - more capable.
The rings that were not hidden were poisoned by the one ring. The darkness poured into the one ring, leaked out through the others and into their bearers. Greed to the dwarves. I think that humans succumb more quickly to both the greatness and the darkness of the rings. Yeah - a fair bit of supposition. Gandalfs attribution of resistance to the ring by the Hobbits was due their race, not their character. They seem to be children of a different Valar - and as such not under the ring. I think Tolkien may have envisioned them as the "wee folk" of the Irish.
In the end, when Frodo fell to the ring, and claimed it for his own, it was the action of Smeagol that resulted in the destruction of the ring. It is a proof that evil, especially the character of Sauron could not live in a world with a copy of itself. It is a demonstration of the self-annihilation of evil. I think that, in a Tolkien world, while there is redemption, it is never cheap. Often, like the case of Grimma, it is accomplished at the cost of ones life. The destructiveness of even a little darkness is very great and it takes a lot of good blood spilled to quench it.
While I agree that the unnatural long life granted by the one ring evaporated as the ring did, I think in principle that Smeagol would have been welcome on distant shores. In an ironic way the thing that cost Smeagol his life, would have counted as sufficient for redemption.
EDIT: If being ringbearer alone was a qualification to go to undying lands would it not thus qualify both Isildur and Sauron to go there? I think there must be some additional or alternative criteria there.