I think it is a semi good idea. It is the only way everyone can be told why they were banned. If you are banned, you can't read PM's, and, if you have opted not to receive emails, then the only way you can get a message from people here is to read it.
I think knowing why one is banned is an essential part of a forum. It decreases discontent, the way I see it. If you come here one day and are banned for no reason you know of(I have witnessed this first hand at forums), you will come here first to see the exact reason. Then, and only then, you will send an email to Thunderfall explaining why you think your banning may have been unjust.
I have no idea as to the inside of the staff forum, but, if a list does not exist there, then mods might pull their rank a bit, and ban who they will, without consulting Thunderfall, or without him ever knowing about it until the poster-in-question emails him in a fit of rage!
Maybe you should create a seperate forum for this list, where everyone can read, but only mods can post. That would be the best way, and would allow it not to degenerate to a list of honor, because most people would be too bored to read anything there anyway! Only offenders would have any reason to go there.
That is my humble advice, and you may take it for what it's worth.
BTW, for anyone that is interested:
Non civ-related forums account for nearly 40% of total posts. That is not counting OT Archive, or the staff forum(s), which are not visible to me. So I'll give it a accuracy pillow of roughly 10%. I think that warrants a higher rating than 'a little conversation'.