Quote - "Not deleting posts and threads is not an option. It's a rare forum..."

A forum that the poser forum management would do well to examine is CGSociety. Their moderators are far more restrict and delete at most one post a month or something like that. Neither do they have any problem with "spambots and trolls". IMO the current policy of this forum is wrong and to the detriment of us all. 

I think the the big difference between the forums is generally those members have been properly conditioned to respond to each other in a civil manner. If members can't be civil to each other, then more moderation is needed. Over the years members here have been conditioned that it's ok to insult someone if they don't like their views, and if you had hit the report button, it would take days for a response and by the time the thread would spiral out of control and eventually get locked.

If you want a less moderated forum, then the members have to moderate themselves in how they speak to each other and not be so combative in discussions. That's not happening, thus the big headache for Ambientshade that he had to inherit.

So what you're suggesting isn't a good idea at this time, but it's a good thing to shoot for if everyone works towards making the mod's job easier.