I think I'm still leaning toward the 3142 layout...

(note, this is a rough approximation of the layout for illustrative purposes only. The control spacing is NOT exact by any any means.)
1) the majority of the time I will be playing 1 player games. In this layout, player 1 is very close to the center.
2) The stick spacing for two player smash tv / total carnage is close to the arcade.
3) for robotron, I can use the player 1 and player 4 joystick and get a stick spacing that is closer to the arcade (10 inches).
4) when playing a game with 3 players (this will probably happen more than 4 players), player 3 can stand off to the left and not be in the way of the player 1 position. The only time it will be cramped is if there are 4 players.
5) I still have the option of creating custom mappings for 3 and 4 player games if I choose...
3 player: 1203 (0 = not used)
4 player: 1234