For better or worse, Support is right on this (for now). Advanced custom graph widget should possibly be called "Aggregate custom graph," the only notable difference between the two is you can use glob in the Advanced config and then indicate aggregate, top ten, or distinct values. And as you've likely deduced, virtual datapoints aren't available for different datasources if glob is in the mix.
We're looking at ways to simplify this, likely offering a "convert" option between the two graph types that would make glob / aggregate available in one mode and make more powerful virtual datapoints available in the other.
