Simon, please move the two deletes (wall and particle) back to the right side. Or even make it accessible via key shortcut or place each as permanent direct access on the right menu. They are too important to hide it in the middle of a category.
I had that in my General Usability Suggestions (Part 2) thread. Nice to know we think alike.
I suggested an entire different category box for the wall types, "d" shortcut to make secondary element eraser, "shift+d" shortcut to make secondary element wall eraser.