Sorry I didn't get back to you on this one yet, Steve.
Yes, it sounds like you need to focus on MultiCore for your app. Although people have been able to make Modules and loaded SWFs work with the Standard Version, this is the Meaning of Life for MultiCore; its raison d'etre.
In the Standard Version the predominant approach has been to do a lot of registration/removal of actors when a Module/SWF is loaded. The problem with this is since all the actors are swimming in the same pool, so to speak, you have namespace issues.
For instance if one widget registers a Notification to a constant evaluating to 'ButtonClicked', then no other loaded apps can use that string as a Notification constant.
Playing with ApplicationDomain can help this, but as you can see, you're jumping through hoops. Trying to fit a square peg in a round hole.
So MultiCore just has a map of instances for each singleton rather than one. The instances are retrieved by key, exactly like you retrieve Mediators or Proxies, so it is a familiar idiom.
Read here: http://forums.puremvc.org/index.php?topic=313.0
about the access of the facade in the constructor which is the primary difference in practice between the two versions of the framework for AS3.