A little busy for me, but I don't do console emus, so I'm coming from a little different veiw. I agree with others that clearing stuff out might help in general, but only have a couple notes or things to test on cardboard mockup of CP.
Are you going to light up your buttons, so only the buttons used are lit?
For the nes button map, I'd use the right most buttons on the middle row instead of the left most. I don't like the buttons I use "buried" inside buttons I don't. A cardboard mockup might help you decide.
MK button map, cool, but what about mk3 dash button? Would SF2 be "better" is it used the mk 5 button plus the upper left button for a curved, angled 6 button layout, instead of a straight offset layout? (FWIW, I prefer striaght box, and I'd prefer the one you show, but some like curved.) A cardboard mockup is a great way to test.
What 4 spinner games are you thinking of? Warlords and ...? Or when you said "each player" you only ment players 1 & 2? (Poblably the latter, as you only draw two.)
Are the joysticks going to be in the way of playing the spinner with steering wheel? Did I mention a cardboard mockup?
Do the joysticks, buttons and TB get in the way of the DOT spinner, asteroids buttons, etc? Okay I won't say it again, but ...
cardboard mockup.
How about 3 player driving games like supersprint, ivan ironman offroad, etc? What about roarty joystick games like ikari & heavy barrel? What about forgotten worlds? (not that you need
every game, but I love these games, and you said as many as possible
)
FWIW, I went the multiple CPs direction, don't have a 4 player CP, and (a repeat) don't do console emus. So I'll understand if you decide not to simplify, etc.