Good for the desktop, but I wonder how a second stack would just stress the joint once the whole unit starts moving and shaking, esp with the extra wires coming out of the top protoboard acting acting like springs. I know this is a bit extreme for most people, but if a ribbon cable connector was available for the USB shield, (with a pass through connectors on in the main stack side) I would be tempted to pot the entire thing due to moisture hazards, as well as structural support.
...Like the idea of having the same shield for through hole AND smd. (though still have not been brave enough tackle smd soldering)