What a great thread/conversation. God I've missed forums!
Loads of great ideas suggested but as had been mentioned the dick's will be dick's regardless of the rules.
My recommendation would be to have more specialist games. Gunman run a skirmish weekend (anything goes within reason) once a month and a filmsim (ammo limits, different medic rules and teams by camo, mid caps encouraged). I've never seen another site do similar, the occasional "milsim" day or gas and shotgun but that's about it. My main moan about gunman is I have attended a few of their advertised filmsim games and they were effectively how they do skirmish days (I've done them when run as filmsim and it's very different).
It's very rare that event organisers are explicit enough about what each event type is and how it differs. For ages there was chat about what milsim is, it never really resolved, people just got bored of the conversation. I'm not encouraging we have that conversation but if organisers put on an event and could list what it is for and what it isn't. Skirmish - hpa allowed, no ammo limits, some respawning in field as per individual game rules. Etc you as the player then know what you're signing up for and I think the differentiated game would draw more players in from further around.
Ultimately I think we are paying for the experience from the day and while sites can't guarantee if you're going to have a good day, they can be explicit about the rules for that event and have events that cater to different groups within the community.
I saw an event recently for just tm recoil owners only, while I could have gone I didn't think it would make the game more enjoyable but it was nice to see the option.