I was at that Burlingame convention on Saturday and Sunday. I'd bought the 3 day pass for 50% off (one day offer, IIRC) as it was cheaper than buying Saturday and Sunday w/no discount. I couldn't make it on Friday due to work and not that much interest in the actors appearing on stage that day.
I'd say most of the visitors weren't in costume. I don't have a uniform but if I did, I would dress up to attend.
I did end up speaking to
https://memory-alpha.fandom.com/wiki/Sean_Kenney at his table. He was in front of his table speaking to me then got behind it. I didn't recognize him and expected him to be older. I asked about how he got the role and if he knew it (as Pike) wouldn't be a speaking role. He knew about what was shown in Disco about the baffle plate rupture incident and seeing himself in the wheelchair but he didn't know about the Disco ep where they went to Talos IV w/Vina and all.
I've been to many Star Trek conventions over the years, and probably my first ones were about 30 years ago.
The best ones to go to in the US are probably the Vegas ones (
https://www.creationent.com/cal/cemission_lv.html). I've been to that two separate years before COVID (from old email, looks like 2011 and 2018). OMG! The # of actors on stage is insane.
https://web.archive.org/web/20180801043631/https://www.creationent.com/cal/st_lasvegas_guests.html was the roster for 2018.
I was in the room when surprise guest Patrick Stewart (wasn't on the roster) came out to talk about upcoming Picard show:
https://ew.com/tv/2018/08/04/star-trek-fans-patrick-stewart-announcement-reaction-video/. Alex Kurtzman came out to talk and then he asked someone (friend?) to come out to explain it further. We were BLOWN away and so surprised and ecstatic!
AGES ago, the Pasadena convention was the happening place but I heard years back, for some reason, LA area Trek cons were basically dead.
The Pasadena one I went to was I think before First Contact was released. On stage, they had ALL the Voyager cast at the time except Mulgrew. Kes was still on and 7 of 9 wasn't hired yet. Then they also had Jeff Goldblum + Brent Spiner promoting Independence Day. They showed a several minute clip of the FX (this was before the movie was released). Majel Barett also spoke but was a boring talk.

I think it was at that convention while we were waiting for autographs in line (they were free back then but the lines could be insane) that some dude came by w/the script of First Contact (wasn't out yet). I don't recall if I read it now but some other people took a look.
The autograph lines were so insane that people would wait for them instead of watching the guest stars speak. I recall they were cutting it off for various actors and then while we were in line, they finished. So, all of us ran to get an autograph from anyone. I was able to get one from Garrett Wang.
Funny enough at the Saturday Burlingame con, Brent Spiner spoke and he brought up the Independence Day Dr. Okun role, the wig and I think how he ad-libbed/added something to his audiition.