A lot of it is a timing thing. I've had some similar experiences. I actually sat next to Mac King for a whole show and couldn't strike up a conversation. At IMX we I sat around a table with Chris Kenner and Lennart Green, the whole time I just wanted to talk with Chris but I couldn't figure out what to say! Finally a kid half my age came up to him asking about his pop out move. It was a great way to get talking with him.
After a show they probably want to move on, go home or take a break. I don't know if that's the place to get talking to them about magic. I think a way to get to their attention would be to just stand out in the magic community. It would take time and perseverance but it's the most surefire way to do it :/
To tell you the truth I get all magician star struck and I can't figure out what to say.