Have you looked to confirm that the stats were generated when you ran a "dbms_stats.gather_schema_stats('schema_name" ??
The reason I ask is because I ran the gather schema stats (on our 9204 database), and it did not gather any stats (I did not spend too much time investigating) ... I just ran gather table stats (since there were only 5 table).
Make sure the stats are gathered at the same level (tables, indexes, etc) on both the instances.