At the end of the day, everyone's going to look at it from their own perspective. Ivan's got to look at from the perspective of running a show, and getting vendors to the show.
If I was a vendor, I'd want the show to be going with all the 'donated' pins on the floor until close, as it means more hours for people to shop. When pins start leaving the floor in the middle of the afternoon, it creates the feeling that the show's over and people are packing up, yet I paid for floor space for a certain amount of time. Having a large amount of vendors there is imperative to the show, so they have to get value.
Perhaps the solution is for their to be an agreement that people bringing pins for free play are essentially 'renting' the pin to the show for the entirety of the show. The $25 early withdrawal fee is just a token fee that many will just pay to get out of there and doesn't have the deterrent effect desired.
It's a fine line... for the show to happen, you need people to bring pins and for them to stay, yet at the same time, you don't want to be too draconian about the rules, or people won't bring them. I don't envy Ivan having to deal with this.