Is there any functionality contained in vacuum that is not contained in pg_autovacuum?
Suggestion:
Modify the base schema for tables and add a timestamp column for the last vacuum operation, and a timestamp for the last vacuum analyze. Finally, a timestamp for the last time that the data was modified via insert update or delete would be handy (but I realize that this timestamp might be problematic).
With that data, a crude autovacuum could be generated periodically whether or not statistics were enabled.