THEME:   phrase with IT subtracted creates an alternative phrase   
GOOD ONES:     "Never mind" [& theme]   FORGET ABOUT IT   
Bear with backup musicians?   SMOKEY AND THE BAND[IT]   
Home of robot jugglers and digital clowns?   ELECTRIC CIRCU[IT]S   
Start to celebrate?   SOFT C   
Acts like an opposite?   ATTRACTS   
Ball focus   BELLE [belle of the ball]      
BTW:   The title, 
"Never Mind," seems to refer to the FORGET ABOUT IT entry, not the theme.  I'd have gone with "It's Missing."      
Average mark   CEE [not sure that it's true in the age of grade inflation]      
Barrie baddie   SMEE [was he bad or just a foil to Captain Hook?]      
RATING:    
 
Three grins = Loved it; Two grins = Enjoyed it; One grin = A bit bland for my taste; One teardrop = Not much fun