Add a subtle blur effect for stuff behind popups/menus. One sample would be when you press escape in main menu. Dialog should pop up, and everything behind it gets blurred. Enables/disables with shader effects in options.
I've always used this in a similar concept in my photography club before I graduated. It really gives it more effect because the foreground and background can be made more or less distinguishable. Ex. Using depth and aperture in photography
it could be disabled/enabled automatically together with the "Shader Effects" option since I'm assuming that this blur effect is most possible with shader...? Also it would prevent us from having more toggles.