One data point about award ticket + upfare and possibility of refund for a cleared upgrade. I did that 2 weeks ago for two people for NYC-LAX-MEL on a Y+ I mixed cabin ticket. Upfared to PP on the NYC-LAX section and then waitlisted NYC-LAX to I class. About 24 hours before the flight, the NYC-LAX segment cleared to biz, United phone agents could not refund the upfare, because they were not sure whether the R fare affected the upgrade clearing (which it must have), As per the phone agent's suggestion, I put in a refund request through United explaining the upgrade and got the upfare to PP refunded. The refund request was fairly straightforward.

Might be worth a shot to check what the PP upfare offer is - economy (or any) award tickets are effectively risk-free. Though, as someone previously mentioned, upfares are non-refundable for voluntary changes.