Well, it sounds like you're saying the only difference between the spammers from the good people is "this nick hasn't spammed us... yet"
There needs to be some way you can either identify is-a-spammer or is-not-a-spammer, and sounds like you don't have anything to identify someone as being in or out of either group until they do it. So since having people get a nickserv account is somehow not an option, it looks like you're down to waiting for them to do their spam then kickban them. But there's a limit to how many people can fit in the ban list, or how much you can limit their spamming by kicking them. In the war against spammers, the spammers are always going to be able to find ways to to evade spam filters unless their grab bag of IP addresses is limited and you can eventually build a list of them to be banned, and I doubt that's the case.
