My layout is real similar to yours, and has worked out well for me. I moved the buttons up slightly so that the extra button (gray on your layout) could easily be used as a thumb button for games like Defender, Smash TV and Rescue. Also, I did away with the separate trackball buttons and made them the bottom row of the player 1 side.
I don't play a lot of spinner games, but I put my spinner down in the lower right below where the player 2 buttons are on your layout.