Select Same Size
The Select Same Color, Appearance, Opacity is quite helpful. Add a new option for Size. The area size of the current selected element would be calculated and then used to find other similar objects within the document that meet that same area size.
A tolerance up or down or range could be provided as well. It would also be helpful to offer a setting for "Select Anything this size and smaller/larger".
This kind of feature would be very helpful when attempting to clean up an illustration generated from a live traced sketch.