I just came back from the Toronto Fan Expo, and as very unscientific as this is, Kate Mulgrew had a line that never ended (until she left early!!), Levar Burton had a modest line-up throughout the day, and Nana Visitor (who was ADORABLE to talk to!!!) was mostly empty.
I wouldn't put their characters on equal footing in popularity, but still, as a simple anecdote, I think it's a bit telling on the levels of popularity. I'm not lying when I say I felt a little bad for her, Nana was easily one of the friendliest people there!