Agree on the first point, we are talking of the auction proceeds. Since this is money that the competitors have willingly invested, there is no correlation with the excess fees, that were a compulsory payment for the application.
However, I disagree on the second point. Once ICANN has calculated the real cost, one of the options is indeed to retroactively refund the difference, assuming that the budget item from where the money comes is the regular gTLD programme, not the auction
funds.
Of course, the obstacle might be that the refund will come a few fiscal years after the payment, but this should not be a major problem
Back to the main issue that originated the thread, I believe that we must also take into account perceptions. So, while I agree that self-promotion of the activities that ICANN does for serving the global community could be done with this money without
affecting the non-profit status (if done properly), I would hope that this activity will be funded by the regular budget.
Cheers,
Roberto