It worked!

Not sure why I'm so surprised, but my script worked fine. So I now have a new calendar called scripts which has a recurring event at 10:00pm to run my script. The calendar is hidden so the "appointment" doesn't show.

Simple!

Talking with Ally, we thought of some variations, but we need to find out a bit more about how to write the script to do them. I'm guessing, but it ought to be possible to set the status to bounce instead of delete and I thought about adding a growl notification to let you know that it was deleting a given number of messages. For me, just deleting the contents of the junk folder is enough.