I'm not buying at this price. A shorthaul upgrade comes in at 95€ or so - the price of a cash upgrade. A sh return (40k) ca 380€. Lh ow upg (50k) 460€ or so.
Also, there is no guarantee, that there will be availability on you flight, than you're so out of luck & cash
If you miss some points for a specific award, than it might be OK to buy, otherwise not so much