Backup-strategy for redundant data in postgresql-db.
One option would be to use materialized views. The main downside there is that at present there's no support for incremental refresh, so refreshing the views would be quite expensive.

Instead I suggest using UNLOGGED tables. That'll skip WAL archiving (and streaming replication) of the data. If you pass --no-unlogged-table-data it'll also omit their contents from database dumps. So you'll basically be implementing your own incrementally updated materialized views over the data.