Was making a test level yesterday and got the urge to write this quick script to make things go quicker - it simply takes all the objects you've selected and randomly varies their height. For example:
Here's a level I made that used the technique:
And here's the script. Put it in your Assets/Editor folder, and it'll show up as a Custom menu item.
Left as an exercise for the student: rotate the objects a random multiple of 90 degrees as well. I'll do that some day...