I don't see this as being a bad idea. I was just modifying some chairs recently and had to delete them one by one at either the legs with the wand or the top down. I went the longer route because i didn't want to delete the base of the entire house and lose what i had built.
Anyhow, i think having a selection cube for deleting is a way better idea because it would be fast, like the wand, and safe, like hammering bricks from top down. This should be a feature added to the new duplicator imo.