What you say lion-g is absolutely true. One of the caveats that I did not mention is that the procedure should not be used if there was a suspected fuel leak, as the Non Normal Procedure for this requires a cross check between the two readings, as you are undoubtedly aware. There could even be a case argued for actually doing it in the event of a suspected fuel leak, but the known error is still being investigated by the makers.
The cynics will say that following the procedure merely re-initialises the FMC to Actual Fuel on Board from the Totaliser, but, in flight, this is not so.
Until the software glitch is repaired, my attitude is to use the prediction (the higher figure) for Vref calculation, and the prediction MINUS the error for Flight Planning purposes.
Regards,
Old Smokey