I have only taken a bus once to a quilt show, and that one was organized by the senior center to go to the Sisters Outdoor Quilt Show. The bus itself was fine, and I would have had no problem going alone, although that time I did go with a friend from the guild. The problem was that we were told to be back at the bus at 3, which was much too early. Most of us were sitting in our seats on time, ready to go, but one person was very late. It was hot sitting on the bus and waiting for one inconsiderate person. Then the driver took a longer route back that was much longer than necessary - I think he missed a turn. After that experience I always drove to Sisters in a private car with friends.
I'm sure most bus trips are better organized than that one, and I wouldn't hesitate to go based on not knowing anyone or worry about the comfort of the bus. I would want to know in advance what time the bus would arrive at the show and what time to be back at the bus, to be sure that time at the show was sufficient. And I would hope that the bus would not wait a long time for stragglers, but would tell them to find their own way home.