I think that they'd be smart to ACT (their profession, you know?) nice - it's in their own self-interest, even if they have to deal with some not-so-great fans at times.
For instance, stand-outs amongst the ones I met were Jonathan Frakes, Connor Trinneer, Casey Biggs and George Takei. They genuinely interacted with fans and seemed happy to do so and were very approachable, even to shy people.
Contrast that with a few of the actors who were not very nice.
Whose merchandise would I buy or who would I go to see in other projects or support?
That's why at the very least, they should be congenial. There are plenty in that group - who do their job in a good humor. You don't have to be a Biggs or a Takei, but don't be a Beltran.
The ones who are either withdrawn or mocking? You're hurting your own wallets.