Best time to hit Le Trapeze is when they have some sort of special event like New Years, Fourth of July, or Halloween. Usually 50 or more couples show up and there is a lot of variety. Otherwise, on normal Friday and Saturday nights it can be hit or miss. Sometimes its crowded, sometimes its not so your experiences can vary widely.
I had been going to Le Trapeze for a number of years with my SO and we stopped going because we felt we weren't getting enough bang for the buck (pun fully intended).
IMHO Supermong has the right idea. There are a number of swinging websites out there and if you prefer to travel alone many of them accommodate that. These sites also advertise house and hotel parties. The sites charge a very reasonable fee to join.
We've had much better times meeting people through those sites.