There are several custom admin pages, reports/views that have been built for Tableau Server besides the ones provided directly on TS.
is a great place to start for some of the user generated content.
With version 8.3, Tableau Server made a Read-only user that can be used for custom reporting from the TS PostGres database. Here is an example of what can be done with this: http://kb.tableausoftware.com/articles/knowledgebase/custom-admin-views-server-access02?lang=en-us
I hope this helps.
I am moving this post to the Tableau Server Administrator section of the forums where you will find other Tableau Server Administrators and more conversations that may be helpful.