I suggest setting up an important feature: This plugin, to release the registration of wordpres, just allowing to create thousands of fruitless users. Thus, it would be interesting an option to delete users without listings in the directory, with a range selection by registration date (like phpBB).
As an example, on my system there by now, since installing the plugin, 1,221 entries. Of these, just over 20 has listings. Many others just pollute the database. As the user panel is not possible to see how many posts each user has is humanly impossible to delete those who have posted anything.
It is important, however, check which users have any post, not just the directory listings. To avoid the risk of deleting important system users as a whole.