Yea, I guess I can understand that, but, if the auction were for a charity that has to be figured in as well. The price paid is not for the ticket but to benefit whatever the occasion was about. The ticket was just a happy side effect of a donation. And $15.00 is $15.00.
1. Make believe that it is the first one used which it could be, and then the individual ticket is worth one day admission, full price. The rest are on a descending scale depending on the number of days purchased. I don't know how much was paid for it, but, it seems that the money was spent on something else and the ticket was just an extra benefit or reward, if you will, for their generosity.
2. Isn't it the same as buying (example) a four day ticket and getting an extra day in the park at no charge at all? One could have donated that money with no perk, and they still would have paid the extra cost of five days. It's not what they bought, it's where the money went. In this case... not to Disney.