I'm not sure that users quitting or emailing admins is going to work. Not enough people care. You said you believe that over 78% are filesharing. Will a network sacrifice 78% of it's users to keep 22% from leaving?
You're probably right. But I'm not necessarily talking about EFnet changing their policy because 20 people say they don't like warez. That probably won't happen. However if 20 people tell the admins they'll leave if warez is allowed on a 100 user network, well then it might work. Granted thats not nearly as big an impact as stopping it on EFnet, but it certainly helps. If 50 of those 100 user networks stop warez, then it helps even more. We (as people who want IRC to be warez free) could even do things to make it worth their while to stop warez. For example I know a bunch of people who go here have websites, if we could get people to agree to do things like have a list of warez-free networks, it would give admins an incentive to stop warez. Meaning if you could have your network displayed on 50+ IRC related websites, in exchange for just stopping warez, you might consider it. Because while the network will lose some warez users, it stands to gain other "real" users. And I know admins like the high user counts, but I'm sure there are at least some out there who would rather give up 100-200 warez bots/users in exchange for getting 50-100 real users who actually join channels and chat.
It's not like it's hard to find warez channels and shut them down. Some networks are unwilling because they don't want to hurt their user stats or they fear some sort of retaliation.
Not even just that, there are other things. For example XDCC clients; programs designed without chatting abilities that just connect to IRC servers to get files. One program is Bottler. All an admin has to do is add a special line to the MOTD file and all Bottler clients will auto disconnect. People can also contact the bottler people and ask to have their server removed from the list.