Without having purchased tickets to ACQUIRE hard cost RDMs or having used affinity credit card spend to ACQUIRE soft cost RDMs, then you would not even have the choice of determining what your opportunity cost of USAGE would be.

Once EARNING the miles are completed via limited and quantifiable RDM sources (BIS, cc spend, bonuses/promotions), THEN all of the fun and zany BURNING valuation scenarios can be trotted out. Whether you can leverage $5000 of 500K of RDMs into 25 'low value' domestic coach awards with retail cost of $4000 or 3 'high value' international First awards with retail cost of $40,000, your hard out-of-pocket cost of those miles indeed do not vary.