SSAS and Visual Studio Optimization Wizard does not work
The answer isn't obvious.

You need BIDS Helper installed to your visual studio. 

There are four buttons in the PARTITIONS tab one of which is the "Edit Aggregations" button.  If it isn't there, you dont have the latest BIDS helper.

An aggregation Manager window will appear, with a treeview of your measures structure.  Drill down to the Aggregations Design folder that appears in that tree, and right click it, or any of its children.  Click the "Add Aggregations from Query Log" menu item, and you will be given a window where you can even edit the SQL that selects your Query log item.  

This will allow you to achieve exactly the same thing that the Aggregations tab currently isn't.  

For the record, the Aggregations tab issue remains, but is irrelevant as this method does everything we need.