Ok, solved my problem. The option for Smart Grid is only available when you actually click the drop down list. That, not the Snap to Grid icon, needs to be turned off by unchecking it. Then you change the resolution, then you can turn it back on (if you want.)
It's a bit confusing because when it's enabled, the Snap to Grid icon says "Smart Grid enabled", so I thought THAT was the Smart Grid control. When it's disabled, the icon says "Snap Toggle Extended".
Hope this helps someone else who may be puzzled.