The comparison between building a Space Elevator and the building of the Erie Canal are not new, but the subject has been revisited here, by TCS Daily. This is a fine article and covers all of the relevant points I believe. He reports an interesting quote from Thomas Jefferson about the Erie Canal project: “It is a splendid project, and may be executed a century hence. It is little short of madness to think of it this day.” But just 15 years later (and two years ahead of schedule) the project was completed. Twenty years after that, it was hard to think of commerce traffic in New York State without the Erie Canal and twenty years after the first Space Elevator is successfully completed, it will be hard to think of space travel without thinking of the Space Elevator.
And in this article, the author calls for more public funding to support such a project.