Characterization of Power Harvester
I'm not sure I understand, but is there a problem to measure directly on Vcap (adding a resistor to load it there, or using the Dset pin and measuring the analog 'Dout' (less accurate resistor, but no boost converter, cap added to Dout))?

If you have the capacitor value Q=CV tells you how much charge is there. E=QV tells you the total energy in Joules. Q=C(Vcap-Vmin) gives a pretty close value for how much charge will be available at Vout if the boost converter is efficient, and E=C(Vcap-Vmin)*Vcap is the energy available for the boost converter.

Other than that, you can probably set the voltage at Vcap externally and measure how efficient the boost converter is. 

And it seems a little bit silly here if the harvester cuts power practically at the same time as it tells you there is no power available anymore. Allthough that function might not be necessary in all applications though ...