If you play "Tron" then it will be hard to play due to the position of the spinner and joystick which required to be used at the same time.
Does one of your joysticks at least have a top fire button? How about pinball buttons on the side to allow playing Visual Pinball ......
See the picture .. this is what I would do ...... since you asked

1) I moved the trackball and the left joystick/buttons more to the left and moved the right joystick/buttons to the right a bit. I also then just moved the trackball a bit lower as well.
This allows you to have more room to use the trackball so your right forearm does not slam into the right joystick shaft when flicking the trackball rapidly.
Not sure why you need five curved buttons (one for each finger ... perhaps) but if you lose the button farthest to the right then you can move the right joystick/buttons even farther to the right ....giving you even more room for the trackball usage.
2) Moved the spinner to the right side of the panel, so you can play Tron and other games which need a spinner and joystick (assuming you are right handed ....)
3) Moved the 4-way joystick a bit to the right, but still allowed for room to use the trackball without it getting in the way.
4) Added more config buttons (all named "Exit" in the photo). I like having "Reset", "Tab", "Enter" and "Exit" buttons present.
PS: Where are your coin up buttons .... are they on the side or something? Maybe you are planning on just using the coin door to have people drop coins into to get credits. If this is true, then I wanted to tell you that I believe that to be frustrating after a while. .... try playing Metal Slug and having to keep dropping actual coins into the coin door toget more life ...

Anyway, if you decide to use CoinUp buttons, then I would replace the "Pause" buttons in my photo with the Player1/Player2 Coin Up buttons and simply add a fifth button the set of configuration buttons I show.
Again, these are just my comments .... I do not care if you sue them or not. I just find it easier to create an image then discuss my ideas since it is easier to visualize what I am talking about when you actually can "see" the changes in the design.
Good luck ... keep us posted on your progress.