Provide the ability to purge or somehow graphically distinguish between reference planes with objects hosted to them and those with nothing hosted to them.
As an additional feature it would be ideal if there was some way of telling what is constrained to what, i.e. if you click on a feature such as a reference plane a list of items that are dimensioned or otherwise constrained to it would be invaluable.
At present if you place a dimension in plan view, you have no idea from an elevation that that constraint exists, it would be useful if you selected it that it was listed or came up in grey with a note to show which view it exists in.
You would also have to take into consideration of that Reference plane had things attached to it or if it was being utilized to cut structural framing.