That's very interesting. Do you know if something similar could be done with Oracle or is it a Postgres-only improvement? I have some old OpenACS systems running on Oracle that would enjoy a boost like that!
That case is purely postgres specific. In general, it is possible that similar cases lurk around at at other places as well.
A good exercise would be to load "old" data into a new schema. Postgres has a --schema-only and --data-only flag for dumping the database. In theory it should be possible to build a new schema based on the modules, save the schema and load the original data on top of this....