I just booked a 1 hour short-haul one-way for 10,000 miles, $350 ticket otherwise. $0.03+ per mile. Booked an 80,000 roundtrip to Hawaii in F class, $2000 otherwise. $0.025 per mile. I see J tickets to Asia for about the same redemption rate when those fares are on sale. Those are all, IMHO, realistic substitutions for paid fares.
Others say they can get a $0.05, $0.07 ot $0.10 per mile for a $10000+ F class International ticket. I wouldn't use that valuation, as I wouldn't pay that much $ in lieu of miles if no award was available, but if that's their choice to value, it's their choice to value it as such.
I think my brother-in-law, who flies quite a bit, is a damn fool for every time he gets 100,000 miles, he books 4 coach tickets to Orlando for his family. He must value his miles around $0.000002 each.
So, to each their own...Based on what their goals and travel needs are.