But there is also presumably value lost by the people performing, otherwise they probably wouldn't have had to be paid so much for the performance. Let's say t

But there is also presumably value lost by the people performing, otherwise they probably wouldn't have had to be paid so much for the performance. Let's say that the two people absolutely wouldn't have done the performance for less than $15k and absolutely wouldn't have paid more than $25k to see the other performance. Then one person is giving up $15k of value to get $20k of value for a net of +$5k and the other giving up $20k of value to get $25k of value for a net of +$5k, so it is really only a creation of $10k of value per performance while the GDP increase is $20k.