The buttons evenly spaced and distributed is confusing.
I'd group them by purpose and maybe use different style buttons that fit their purpose.
I like the smaller view buttons across the top.
Maybe use triangular buttons for shift up and down if that's what the buttons on the right are for.
The gas and brake should probably be next to the shift buttons so you can use the same hand for both.
You could put them side by side like pedals to keep everything from forming a square with the shift buttons.
Maybe use green and red buttons to make their purpose clear.
What are you doing for coin and exit (ESC)?
Maybe get a rectangular button for the coin input and make a label for it that resembles a coin slot.
The square and rectangular buttons usually pop apart so you can insert labels (they were usually used on gambling machines).
The button you use to exit games should be away from all the others and it's function made obvious.
I guess you could do a combination for exit, but it can get complicated with other emulators and PC games.
Labels on the CP art might help if you plan on sticking with regular arcade buttons.
Here is my old CP with homemade paper inserts in the buttons. More recently I've been using clear inkjet labels.
The big thing is knowing exactly what games you want to play and what you need to play them.