I've been reading most of the posts in this thread now, and although I've never been to a con myself, I'll just add my two cents anyway.
I agree with those who said earlier in the thread that maybe having sky high expectations before meeting an actor is a great way to set yourself up for disappointment. I've seen a lot of comments about how actors aren't personal enough, don't take enough time to chat with everyone, are just in it for the money and so on. And honestly, what did you expect? For the bigger stars the lines to get an autograph can be several hundred people, and I imagine that the actors are on something of a schedule, they can't just sit down and have a 10 minute chat with everyone because the last half of the people in line wouldn't get their signatures at all. And of course they do it for the money, what else? As in the case with the TNG stars for example, it's been 20 years since the show ended, you don't seriously expect them to still be thrilled enough at the prospect of talking to fans about costumes or plot details after all this time, to just do it for goodwill, do you? I can absolutely understand that it gets tiring, especially as I imagine that there's a relevant part of the visitors who make it very clear that they're just there to get signatures for their collections.
I'm not saying that it's too much to expect an actor to at least say hi when they're approached at the signing table, but from what I gather, there are a lot of people who have no idea how to act normally around famous people/people they admire/ people in general.