I agree, more than 4 buttons for players 3 & 4 may seem overkill, but the way I am looking at it, next gen consoles will be emulated soon, which will require more than 4 buttons. I went a little overkill... My 4 player panel (loosely based on the SlikStik QuadStik) has eight buttons per player... Overall dimensions are 48"x22".
Put on a cabinet with a 27" TV, and it seems normal.