Bearcat
In addition to D & D themselves positively encouraging Practice Pans, the standard student pilot text on RT (Trevor Thom volume 7) also suggests this too:-
"You should make a practice call at some stage during your training; the experience will be valuable should you ever need to use the service in a real situation".
It then goes on to cover, in detail, exactly the points you raise about how to make sure you don't step on a real emergency. And in the JAR PPL exam you get tested on this.
Perhaps someone from D & D could tell us what the average numbers are for real and practice calls in a given day.