You can't directly create such a role in Alfresco today. Alfresco does not have a tiered or delegated security role model, such as would be found in enterprise systems.
It is possible to create an Alfresco application that can be run by a non-administrator (with permission) that will manage users and groups. It might be done as a Java-backed web script that escalated privileges for the application to manage those types of nodes, and replicated the Alfresco user interface.
Here is another method that might be more feasible for you. If you authenticate your Alfresco users against LDAP or Active Directory, and you have an identity management application to allow you to configure users and groups, then you would have solved most of your problem. Managing space users from a non-admin account might require a Java-backed web script.