Ciaran,
that sounds like a good course of action to me. If I'm not mistaken OpenACS core team members such as Dan Wickstrom and Don Baccus have argued all along that the forums package should have used the content repository.
I can't really give a good estimate on how much work is involved in the change. If you decide to do this, you might want to look at the bug-tracker package for reference as we upgraded it to using the CR recently. The relevant upgrade script is:
bug-tracker/sql/postgresql/upgrade-0.9d1-1.2d2.sql
Don't be deterred by the size of that upgrade script as it did a lot more than just the CR upgade 😊
