I'll sing to get the party started but I won't sing if I have a decent sized rotation. If I get folks on the playlist before I start the show, I won't sing all night.
The way I see it I provide two services for two different groups of people. To the club owner I'm a liquor salesman, to my singers I provide a platform for them to sing and sound as good as possible. As a musician I have gigs where I play guitar and sing to get my "fix", my singers don't so I give them as much stage time as possible.
Very seldomly do I have to run a non-karaoke track during a show. I'm sure this is not the case for eveybody, (we all have to adapt to our audience), but it works for me.
Jim