Here's what I think, and this is nearly 100% conjecture, because I refuse to read Vice, and have for a long time. I think the mystique is something like this: "The world is a joke. Only we get the punchline, but we're going to let you in on it one article at a time." After reading Vice, people come away with a sense that they understand why the world is as dysfunctional as it is. People like simple answers, and people like knowing things that other people don't know. Vice wraps both of those in a tiny little package with a ironic bow on top, all couched in a language that is meant to offend the easily offenable. My guess is that Vice's readership is mainly formerly sheltered college freshmen whose eyes are just being opened to the world, and who don't really like what they see.
Everything you said could apply to Jon Stewart, Steven Colbert and John Oliver, which is why I don't watch them. They essentially create a class of liberals whose only source of knowledge is from semi-satirical, purposefully-inflammatory TV shows. Just an aside.
It's hard to blame kids for being cynical these days. Vice preys on that. The future must look bleak to today's college freshmen, as the economic downturn happened when they were in 6th grade, and 9/11 happened when they were in kindergarten. That is, before most of them could ever have paid attention to the world. Shitty news is all they know. I'd have a negative worldview, too, I think. In this light, Vice's ascent makes perfect sense as a reaction to the world and all its ills.
Well, I wouldn't say that Vice's ascent is based solely on its "news". It's a "cultural" magazine, of sorts and is plugged into all kinds of stuff and they were early promoters of brands like American Apparel and are involved with shit like The Creator's Project. What I'm talking about is that the snarky rag it used to be has become something that people look to while forming their early worldview.
People look to VICE because they see it as better than a FOX News or a CNN. When the mainstream news channels look really unreliable, it is easy to sneak under the radar with a news outlet that is "not as bad." You can be snarky when something like FOX News is running about.
I don't mean that bad news has appeal. I mean that the wold has had a very dark hue for more than a decade, which has created a condition in which publications like Vice have become attractive. The culture itself is darker. You see it in other aspects of pop culture. Nihilist comedy seems to be popular right now. I think that's another expression of this trend. Nothing matters. Nothing's sacred. Skin deep is as far as it goes.