It is one thing to say "Something must be done!" with a tone of righteous superiority. It is another thing entirely to specify what must be done. Many of these risks do not seem existential to me, some (like dystopia) should really be properly buried as ideas (Bostrom actually dismisses this idea in that paper). The ones that do seem realistically existential seem almost impossible to prepare against on any realistic scale - aliens, gray goo, uploads, and massive global warfare/conquest don't seem like they're going to be sensitive to many investments we make now, since they're either too small and specific or too large and non-specific to address generally.

You also forgot to list the biggest problem: "Something Unforseen."

It's not terribly constructive to say we lack good self-preservation mechanisms without at least hand-waving what good self preservation mechanisms might look like and how we could theoretically try to start having them. The mere fact that we could all die at any moment is not much of a cause for alarm if there's really nothing we can do about it.

Edit: My general point is clarified in a response to a response to this post.