I like the location of the spinner. The look of it isn't so aesthetically pleasing, but it's VERY practical.
The buttons concern me though. Being at an angle would cause the players to stick their elbow out a bit. It's not an issue with the player on the right, but the left player would most certainly jab the other player more easily than if it were straight. It also makes me tend to turn my body a bit left while playing (to make them straight while I am playing) which would throw the joystick off since it's straight up. My advice, keep them straight. Or perhaps if you MUST have them ergonomic, maybe a curved layout would suffice.
Also, keep in mind if you are getting this done through MAMEROOM and you are planning on using the Turbo Twist 2 from Groovygamegear.com, you'll have to put a button in place of the spinner knob in your final layout, since the TT2 fits into a standard button hole. The worst would be if you were to order it with the standard spinner hole (bigger) and then the TT2 wouldn't fit. You could always make the hold bigger, but not smaller with a drill.
Good Luck!
DeLuSioNaL