I've met quite a few Trek actors at cos over the years, and not had a bad experience.
While my ex-wife and two eldest kids were watching Jon Pertwee give a talk in Bristol, my daughter nudged me and whispered "It's Q!" I went to correct her, only to realise she was indicating John DeLancie who was sat just behind us, drinking coffee and watching Pertwee's talk. He winked at her when he noticed her looking.
Walter Koenig toyed with me at Cardiff. I was running late, had no breakfast, and hurriedly grabbed a pie before entering one of the halls. Just as I grabbed a huge bite, I realised he was on stage, and they were announcing competition winners, and it was me! I had to go up on the stage, pie in hand, trying to chew, and the grin on his face was priceless, as he started asking me questions!
Nana Visitor, Ethan Phillips and Robert Picardo were all great.
Best non-Trek experience was London MCM Expo last year, got a pic from CCH Pounder, and when I asked her to sign it to "Gaz", she wanted to know what it was short for, and where I got the name.