I agree, put some border stuff around the controls.
To break up the pattern a bit. If the trackball is going in the center of the CP, I'd put something interesting around that as well. Make it the focal point of the CP. Since you are going with that specific side art design maybe around the trackball you could put the atoms circling it but in a different color to break up the blue a little then have the same color border around the buttons. Also, around the joysticks you could put directional arrows in the same color. Then put the Mame logo somewhere on it as well. Try to incorporate the joystick colors into the design if possible so the joysticks don't look out of place when looking at it. The graph design is so linear, I'd use as many curves as you can to keep it from looking blocky. Plus, it will look natural with the graphic curve to the CP background.
Just my opinion (I'm not very artistic but I figured I'd give it a shot)