One of my goals of the ACS was to get an autograph from E.J. Corey and Roald Hoffmann. I got neither. I was stricken with guilt when the time of their appearances coincided with a couple of talks I really wanted and needed to go to. I gave in to my guilt and went to the talks.
The registration fee for the ACS convention is a rather steep $385. Throw in a hotel for 4 nights for at least $800, travel at about $200 (from MN) and food etc... The final total can end up close to $2000. Granted, my employer picks up the tab, but for my small school, $2000 is a significant amount of money. I could use that $2000 in a lot of different ways (like research).
The bottom line is that, I couldn't squander the (expensive) opportunity to learn and advance myself as a teacher, just to get a few autographs. The autographs would be really cool, but in the end, they are just ink on paper. I chose knowledge in my head over that.