Yes, the PostgreSQL repository does contain the information. The data_connections table holds information on all the actual connections to data, and defines whether they're extracted or live. The fields owner_type and owner_id are "Workbook" or "Datasource" and the ID of said workbook or datasource from the workbooks or datasources table, respectively. So that will provide you the basic information you need for what content uses live vs extracted connections.
The historical_events table, and the hist_* tables that can be joined to it, describe who has done what, with what content, when. It does not, unfortunately, contain any performance data. But it will give you what you need in terms of how actively each piece of content is being used. Performance information can really only be extracted from the http_requests table, and can be a bit flaky.
You will likely want to export this data incrementally to some other database system, as http_requests is trimmed at 7 days by default, and historical_events at 180 days.
The column is Has Extract, and you can create a filter to manager both, True for Extract and False to Live.