Along these lines, I've been thinking of modifying the page so that there's a block of text (similar in look to the Nupedia attribution requirement) that says something short and to the point. "This is a User Created Encyclopedia. Click <a>here</a> to learn how to contribute."
When they click there, they get to some of our pages about how to contribute, how to make pages, etc.
Other ideas would be: "Wikipedia: The user created encyclopedia with 2,173 articles! Click <a>here</a> to learn how to contribute!"
Where the count is updated automatically from time to time.
I think either of these would be an improvement. Probably the most suitable existing starter page is the one you wrote:
http://www.wikipedia.com/wiki/Welcome,_newcomers
It's now a general introduction, with links to other introductory material.