I think you raise a valid point. But it's not surprising. Put yourself in the places of the nine people who will become the Fellowship. The habits of a lifetime are not changed by a single day's committee meeting! (Even if it's chaired by Elrond!)
Pippin and Merry are basically still very young -- think of them as frat boys. They're along out of loyalty to Frodo. The Ring is magical, but it doesn't really affect them -- they aren't tempted by it, for instance. The only thing that really seems to get to them are the Black Riders. (Can't blame them!) Otherwise, the trip is still something of a lark. (They do grow up a lot later on, but we're talking earlier.)
Boromir went on the trip to Rivendell in hopes of finding salvation for Gondor. A Gondor that believes in swords, not magic, a Gondor that no longer has a connection to the Elves, and a Gondor where Numenor is a distant legend. (The 3000 years since Numenor foundered is a long time.) He didn't really know what Rivendell was or what to expect. Elrond wasn't a legendary figure of great wisdom, but forgotten by all but a few lore-masters.
Also, note that Boromir had arrived in Rivendell the morning of the Council.
Furthermore, Boromir is a man of action and not notably contemplative or self-analyzing. He went to Imladris hoping for something to save Gondor and found midgets carrying a ring which he's told is a powerful lost thing of power. Why should Boromir be particularly impressed? It's easy to imagine him being impressed with Rivendell's beauty, but thinking, "I could take this place with a hundred good soldiers of Gondor. How can they help against Sauron?"
Finally, once it is made clear that the Ring can't go to Minas Tirith to help, his mission has pretty much failed. It's not clear how much he believes in all this, anyway -- it's a bit like Winston Churchill in 1939 being sent in a dream to somewhere in Wales to seek help and upon arriving meeting Merlin and getting told that Arthur is heading off to destroy Excalibur and would you like to come along? Would he say "Sure!" or just back away slowly and carefully?
Gimli and his father show up at Rivendell because their home has been threatened. They do know of Elrond and Rivendell and do know that there is still magic in the world, but they are craftsmen and warriors and are still hoping that this is all just a misunderstanding or something, so they can go back to rebuilding the Dwarf Kingdom. Furthermore, while they know of the Elves, they don't trust them. Dwarves and Elves have been mutually hostile for at least 6000 years. Dwarves may respect Elves' power, but they probably think of them as effete remnants of the great fighters of old. When the orcs multiply it's the Dwarves who go off and fight them, not the Elves who hide in Rivendell.
So they come to Rivendell for advice. Not because they think Elrond is ultra-wise and certainly not because they expect to find Gandalf there, but because they know that Bilbo -- their friend -- is living there in retirement. And when they get there, they get the Ring dumped on them. "So," they think, "is this real or some Elvish trick?"
Gimli goes along as much as anything for the pride of the Dwarves -- if the Elves are on this trip, the Dwarves need to be part of things, too. Doubtless the Dwarves have more belief in magic/supernormal than do Gondorians, but it's not part of their modern life, either.
Sam is there for Frodo. Period.
Legolas seems to me to be focused on the Ring more than the others are, but as an Elf, the reality of the Ring is probably more convincing to him. But, again, he's not a High Elf -- he's of a branch of the Elves who started out for Valinor long, long ago, but never made it, and who have ruled a forest kingdom of Dark Elves since the First Age. Think of him has something of an unsophisticated country cousin. (He was in Rivendell as a messenger from his father, the King of the Elves of Mirkwood -- presumably not on an errand connected with the Ring or Sauron or it would have been noted as it was for Gimli and Gloin.)
Aragon is the one (other that Frodo, of course) who is personally committed to destroying the Ring. From his long association with Gandalf, he understands that it's real and dangerous, and he understands that magic is real and that Sauron is terrible and powerful and probably not to be stopped by arms alone. But even he is conflicted, since if it were not for the Ring, he would be off to try to save Gondor. But he makes it clear that he is fully committed.
Given the people involved and their backgrounds, how real would this quest be? It requires a lot of trust in the wisdom of wizards! How many of us if we were summoned to a Board of Directors meeting at work and told by the company's chief scientist that they had found a nuclear bomb in the basement and we needed to set off on foot carrying it to the Nevada Test Site to dispose of it would say, "Sure! Great idea! I'll get right on it."
Frankly, I think it's amazing that so many people were willing to do as much as they did!
So prior to the events at Rauros, Boromir is planning to head off to Gondor, Frodo, Sam and Aragorn are heading to Mordor, Pippin and Merry are wondering what they're doing there and thinking that they'll stick with Frodo. Legolas and Gimli are more aware of the dangers than anyone but Aragorn and willing to follow Frodo, but must be thinking how hopeless this all looks and wouldn't it be great if we didn't go charging off into the clutches of Sauron?
Once Frodo breaks the Fellowship, everyone does what it perfectly in character for them.