Few items..
1) remove the mouse buttons. I can't you being able to use them with the trackball or the spinner. Just have them use player 2 buttons. If you want to keep the mouse buttons available for windows, the just have player 2 buttons 1 - 3 be the mouse buttons.
2) dont - DONT - add the player 1 - 4 buttons on the top right unless you can disable them. WHY? your playing street fighter alpha with your best friend... your kickin some ass and have him stunned. your running up to do some special move... and he grabs joystick above him and you start moving in the wrong direction.... then he hits extra buttons so you cant get your move off. REALLY this happens! all fairs in love and war when beers involved!
3) Make a mockup with cheap wood (you can get press board from home depot for like 4 bucks for a 4x8 sheet. Its crap but it works for testing a layout. Then try it. I think you might have some trouble with your spinner... but I LOVE the look and if you can get away with it I think you should keep it if at all possible. but if you hate using the control its not worth it. I'm worried aout the 4 way and the joystick+fire. I think the player 1 and 2 joysticks will get in the way. You want to be able to lean on a control panel sometimes.
It might work out with removing the extra buttons at the top (where I would see them being useful with the 4 way not so much on the joystick+fire) so maybe add a button or two over there. Then move the joy+fire to the right some so your arm goes to theright of player 2 joy (since I bet you will use that with the spinner or the trackball most often. Its really too bad you cant buy the top fire wico ball tops anymore. They would make it so you could remove the joystick and everything else I think would fall into place. I would also move the coin and start buttons on both sides. Who was making those again? They might be able to tell you how the did it..
Anyway, I think your artwork is GREAT and I like the bottom 1/2 in design. I just think you aren't going to be happy with USING the top 1/2... even though it looks REALLY cool.
(btw, consider hotswap?)