I have mixed feeling about side art.  You don't play the cabinet, you play the control panel / screen.  And in an arcade with machines lining the walls - you can't see the side art anyway.
So who cares?  Same thing as pinball machines - collectors are always going nuts over the cabinet condition - they they line them up side by side so you can't even see the cabinet artwork!  /sigh
That being said, I think an all black cabinet is not the way to go.  Needs something to break it up a little.  Something as simple as colored t-molding usually is enough.
But that's just my opinion.  
