How to clean the Contacts and relevant Users
You could use Search > Search Builder and search for Individuals whose First Name and Last Name are NULL (when this is the case, Civi will use the email address as the Display Name), select all of the search results and then create a Smart Group. You would then periodically review the contacts of the smart group by navigating to Contacts > Manage Groups and then clicking on the Contacts hyperlink to the right-hand side of the group and perform the desired actions.