Ok, many commnets from me.
IIRC, the extended version of the third movie shows Denethor using the orb and showing it making him crazy. That's a pretty important plot element.
(And that's another bother of mine. To the best of my recollection, Aragorn never reveals himself to Sauron by way of the stone in the movies. It's one of my favorite bits of the whole thing, even though it happens "off-stage.")
No, the extended edidtion doesn't show Denethor using the Palantir. There's never even a direct statement that Denethor has one, just a hint when Gandalf first meets with him at the beginning of RotK: "do you think the eyes of the White Tower are blind?" We do, though, see Aragorn use the Palantir in the extended edition to more or less call out Sauron. He goes infto the throne room alone at night, takes out one of the Palantiri holds it up in his hand, looks into it, Sauron's eye appears, he shows Sauron his sword, and basically says I'm gonna get your ass before Sauron freaks him out by showing him an image of Arwen laying weak in Rivendell with the grace of the Eldar having left her now that she's chosen to be mortal.
As for Sam an the Ring. I'd say he has to be affected by it at least a little. Hobbits are a most resiliant people, it takes a longer time for the Ring to wear them down, which would be why the Ring doesn't bother Sam as greatly as it does other people, but given enough time, it would wear Sam down too just like it did Frodo. The whole grand statement of the story is that when presented with domination over others, eventually everyone would fall to hidden desires for it; thus Frodo claiming the Ring for his own in the end.
About
Tom Bombadil. As for the argument that he's a Maia, I quote:
One popular theory is that Bombadil is a Maia, as Tom seems to have unlimited supernatural power inside the boundaries that he set for himself, and perhaps the reason why he has such powers is the fact that he is content to live within these limits. "Eldest, that's what I am … Tom remembers the first raindrop and the first acorn … He knew the dark under the stars when it was fearless — before the Dark Lord came from Outside." The Dark Lord Bombadil refers to is probably Melkor and not Sauron[2]. But in that case, Tom was already there even before the Valar entered the world, dismissing the theory that he is a Maia. In addition, he is eager to protect the Hobbits from danger within his own domain, yet is completely indifferent to the threat to Middle-earth as a whole, which is paradoxical and also uncharacteristic of a Maia.
I side with GKE on this. Bombadil was just something else floating around in Tolkien's head that he shoved into the story there early in the story before he had anything resembling a clear idea of what the story would be like. Scholars studying his works point to how the beginnings of FotR are so different in tone from what comes after those beginnings, and this difference is why I think Bombadil was included. He fit the jaunty tone of the beginning that still was a little bit
The Hobbit-ish. I've also read that Bombadil's look was based on a stuffed toy that Tolkien's son had. So, there's that he's included because Tolkien enjoyed playing with his son with that stuffed toy. And finally, I offer this quote:
In reference to Bombadil, Tolkien himself said that some things should remain mysterious in any narrative, hidden even to its inventor....
I think Bombadil is indeed something Tolkien put into the story without a clear idea of what Bombadil was, and that he didn't know didn't bother him.
I absolutely hated what he did with Arwen.Glorfindal was way cooler....
I actually liked that they collapsed Glorfindel into Arwen in FotR. It gave her character something to do other than stand around and be all princessy, and barely there doing that at that. There are oh so few female characters in LotR, and giving Arwen Glorfindel's rescue in FotR gave her more screentime. Additionally, it truly helped with the problem of converting the books to the film medium as it removed yet another character that would have to have time spent introducting. The same problem comes in why Elrond's sons and the other Dunadain rangers are left out. Sure, every character in the books could have been shoved into the film, but then people unaquainted with the books would be lost going, "Who's that again? And who's that? Isn't that that other person?" and on and on. Never underestimate the average person's inability to tell the difference between fantasy and scifi story characters. By limiting the number of named, important characters running around, it helps streamline the story just a bit and make the story more accessable to average people.