Guidance on data-transfers between cubes?

Going off your idea with the export....You can set up a data mgmt export sequence data source and connect your data mgmt export sequence to that. Then attach that data source and corresponding transformation rules to a workflow import profile. When you click load and transform on that workflow import it will kick off the data management export and reimport that data. Want to get on a webex tomorrow morning? I can show you how to set this up pretty quick! We actually did this at Structure tone at first for transferring the data from the people cube to the main cube before they trashed that idea if that rings any bells! Not sure if it's the best practice but it works..

I would say there are some factors to consider as to which method to use.
Execution: Is this a central execution that needs no particular oversight, or is it something each WF will be doing for their subset of data?

Audit Trail: Do you need a detailed Audit Trail, or is this just a 1 to 1 opy of data?
Maintenance: Maintenance going forward will be either all UI components, or sit in a BR, so who needs to maintain or possibly troubleshoot?