User Registration, only registered users can create a site

In the Wordpress Network settings, there are four main options for Registration:

*Registration is disabled.
*User accounts may be registered.
*Logged in users may register new sites.
*Both sites and user accounts can be registered.

I only want registered users to be able to register for a site/blog, BUT I want anyone to be able to register for a user account.

Is there a setting I'm missing?