I'm a huge fan of Kevin Smith and invested over £100 each for my wife and me to get a Diamond pass. Honestly, it was one of the best decisions I ever made, because he is a hero of mine, and he was amazing. Held his arms out for a hug like we were old friends.
However not ALL guests will be like that. Some of them insist on no contact etc, and you only find out when queuing. There are some horror stories around this, and you can dig it out if you look hard enough.
I know that Wil Wheaton has germophobia, so wouldn't shake hands, but everyone was made aware and he still posed for great photos with people from what I saw.
However, this is usually the minority, and most guests understand its a big deal. Rob Zombie once said "it's a few seconds of my life, that I'll likely never remember, but for fans, it's a few seconds and they will remember it for the rest of their life". It's nice that most subscribe to this philosophy.
Personally, I prefer a photo over an auto.