Lookin' good! Here's what I think.
I think your marquee should have the original one you posted with the Nintendo vs Sega text with full color background. Don't use transparency, it looks great as is. But I would add some characters in the foreground to over lap the text to give it a more 3 dimensional feel.

But your control panel can have this graphic, but without any text: (just Mario on the left with the background and Sonic on the right with a background. Remove the logos and the V can be replaced with a blur effect to merge the two sides.

They would both tie in perfectly. Then for the side art, you can have a rectangular sticker of a full body shot of Mario on one side and a full body shot of Sonic on the other. Perhaps text below it in small print saying: Nintendo vs. Sega.
D