I'd address the points left for me by VG, or in addition to what he has said:
1. Posts are the only way for us to track user's history and activity. There is no intention to provide the ability to delete your own threads. This also helps us deal with those who might want to try to cover their tracks by removing their content.
3. I equally like this idea. But we don't have to limit it to a vBulletin plug-in. I welcome any other products we can install in top of it, as long as we can integrate the membership database. If you can find a software that will do the trick, link us up!