It is quite painful to go through this import/export process and preserve all relationships between records (parent/child), and also all activities (and custom activities you might have)... The closest thing working is the OData dataflow path, and still you have to take care to synchronize/run the parent dataflows before running child dataflows... Takes time, you make mistakes.
Anyways, would you please consider to offer a functionality to Export a complete 'data snapshot' of all entities (or a selection of them) in an Environment (A), the we can then be able to import that 'data snapshot' into the new environment (B)? Probably as an option when Exporting a solution? In that sense you would have on one hand an exported solution (managed or unmanaged) + a complete data snapshot of your environment that you could import to the new environment in a single shot.