One perspective is you can fly domestic first (low award) for 40K which on average is about $800 buying outright so you would be paying twice that.
Its not necessarily true the "you would be getting those miles back" argument if the amount of PWM you use brings it down to what restricted coach cost as you are paying coach prices to get first RDM's and MQMs and there is some value to that.
It's much less attractive for intl as you would really have to use over 100K miles to get it down to what coach costs, but for this year at least you do get 13K RDM's (as FO) versus 8.6K (additional 4.4K) whereas next year you actually would lose 7K (netting 10K). So this year it would cost 36K miles to use PWM and next year it will cost 47K miles.