Using the cost of a mileage run ticket versus the MQM's earning gives you the cost of the MQM's not their value. Once you have made Diamond status extra MQM's have no value except for any bonuses that may or may not be offered.

The question is how much is the higher status worth to you. If you are a big person or very tall the wider seats in the forward cabin may be worth more than someone a lot smaller flying on their own dime.