if playing along with the singer is acceptable in your club, flora, it does seem odd that you were not allowed to either sing yourself, or play a tune. if on the other hand, the singer gets a double go, I can understand that the mc might consider it unfair to the other performers, especially if at a venue with a 11 pm non negotiable finish. I guess only you can decide if it is worth going or not. I think that sometimes an event that mainly consists of players/singers can be a victim of its own success, as it might not be considered attending if you don't get opportunity to play much.
if you were able to get to footscray,[ presumably out of your area ?] any muso joins in with any song, providing no one asked they don't play along with them.