The key metric you need to ask yourself is the maximum $$$ you would pay BA for Club over the coach option you would otherwise fly?

Would you pay $100 more for BA Club? $500 more? $1000 more?

At what point would you say the upgrade is not worth the $?
The $ amount right below that is your maximum and how much the upgrade is really worth to you. If you would pay a maximum of $500 more, you are getting a value of $500 for those miles.

The value you get from miles in a particular redemption is not normally what they are worth to you. You should attempt to only use miles in circumstances where the value you receive from them exceeds their worth to you. Sometimes the gap will be big, other times small.

Opportunity cost should be the primary factor in determining what miles are worth to you. If you do X, you cannot do Y with the miles. How much are X and Y worth to you?

Take two business travelers who earned 500K miles from travel for their employer.

Business Traveler A:
Lives in STL. Feels like he travels too much already. The only place he wants to go is to DFW to visit his sister several times a year. He isn't close to anyone he wants to give his miles away to. He redeems 25,000 miles 4 times a year to visit his sister in Dallas. Deep discount tickets in the market cost around $150 and he would have bought these tickets. So for him, his 500,000 miles are worth about $3000. (20 ticket x $150 = $3000)

Business Traveler B:
Lives in STL. Enjoys an exotic vacation every year. On average, he uses 100,000 miles/year on tickets that would have cost $2500 (deepest discount). He would never have paid $2500 for these tickets if he didn't have the miles but would have paid up to $1500 cash for these tickets to these places he wanted to go. Business Traveler B is getting $1500 value from 100K of his miles, so his 500,000 miles are worth $7500. ($1500 x 5 = $7500)

Beaubo - lets say the employer of Traveler A paid $25,000 for his tickets each year.
Meanwhile Traveler B's employer only paid $8,000 for his tickets each year.

You would tell me that Traveler A's miles are worth more than Traveler B's miles because of the cost of the tickets? Even though Traveler A will use all 500K miles on tickets that he would have paid $3000 for while Traveler B would have paid $7500 for the tickets he redeemed his miles for?
The majority of BIS miles earned are because individuals are already traveling on a particular itinerary and want to earn miles while they are at it.
How is this different from the folks that are already spending and want to earn miles while they are at it?

Both scenarios have opportunity cost.

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Some expert MRs consistently earn RDM for half the cost they would pay for the tickets they use the RDM on.
Example:
Expert MRer earns 500K RDM at a cost of $7500.
Expert MRers has specific flight needs they would have paid $15,000 for.
Expert MRer redeems the 500K RDM for the flights and pays $0. (Ignore taxes for simplicity)

IMO, the Expert MRer got a value of $15,000 from the miles. Not the $7500 they paid for the itineraries they flew.

If the Expert MRer's friend wants to use the 500K RDM, should the Expert MRer consider he is giving his friend miles worth only $7500?

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Those who say they get a $14,000 value from an F ticket to Australia are fooling themselves.
Unless they would have paid $14,000 for that ticket if they had no miles.
Again, the value of those miles they use for that F ticket to Australia is the maximum cash $ they would spend on that ticket if they had no miles. If they spent 150K miles on a ticket they would have spent a maximum of $3000 cash for, they are getting a value of 2 cents per mile.

A person who has more trip needs they can use miles on should value their miles in their accounts higher than the person who has less potential trips.

If person A has 500,000 miles and can only forsee trips that will use up 400,000 miles, they should attempt to use miles on every trip, even those that cost little cash and are a poor use of miles.

But person B who has 500,000 miles can forsee trips that will use up 4,000,000 miles. They should attempt to determine which of these trips will save the most $/mile if they use miles instead of cash. They should maximize the use of their miles and buy all of the tickets that are a lesser use of miles with cash.

Miles are worth FAR MORE to person B than person A.

It does not matter what person A or B paid for their miles!