If a user has made enough edits to articles that they are able to move pages and edit semi-protected pages, they have contributed enough that they should be able to create a userpage. Userpages should be reserved for those who are writing the encyclopedia; WP:NOT a webhost.
I think this would have unintended negative consequences. When I register an account at a new Wikimedia project one of the first edits I make is usually to my userpage to let people know where I'm coming from and where I can most easily be contacted.
In my experience we don't have a lot of newbies starting out with building a userpage. Typically the people who build a userpage early on are veterans from another Wikimedia project. Take this contribution log as an example I happened to notice:
http://en.wikipedia.org/wiki/Special:Contributions/J%C3%B3na_%C3%9E%C3%B3run...
This user is an admin at the Icelandic Wikipedia and her main interests are probably to contribute there. She registers an account at en to add interwiki links and make some incidental useful edits. One of the first things she does is to build a userpage with a bunch of userboxes.
Now, some of those userboxes I think we could do without. But I don't think it's accurate to say that contributors like this are "using Wikipedia as a webhost".
Regards, Haukur