Thanks @korchev for your reply.
As I said there are complexities I likely don't understand.
For example, it's unclear when I can use ${data} and when I cannot. I gather it's available for components that contain items. So I learned something today. 
I understand the unique naming requirement on nested templates. But instead of the magic property, could you not create a page property and then the collection would exist in the Data drop down?
For example, I have Shipments HasMany ShipmentItems HasMany ShipmentItemDetails. I added a second nested grid via RowExpand and Set Property. This results in the Data drop down showing Master (Shipments) and the 2nd Child (ShipmentItemsDetails) but not the middle child.
It seems if it were a page property it wouldn't be the exception.
Josh