I'd have to agree with the busy thing. also, you might want to consider lowering down to 3 buttons to the wings (players 3 and 4), as no game that i know of requires that many buttons for a 3rd and 4th player. you might want to keep the locations the same, so that if you need to add them later (gauntlet legends) you'll be able to. I'd also just use 6 buttons for players 1 and 2, as it's just as easy to remap the buttons as 4, 1, 2, 3 for use with 4 button neo geo games. you can never remove buttons, and very few people would argue that you can never have too many.
as far as using the screenshots, i'd recommend against it. I've never seen the screenshots done tastefully enough that i'd vouch for putting them on the outside of a cabinet anywhere. maybe if you made them really dark, or really light, and then put instructions or a logo in the foreground. That might actually end up quite nice. make it hidden detail, and i think you'll be much happier with it in the long run.
all personal opinion. i'm sure some people would consider my cabinet bland...
-dave