I proposed a revision to the rules a few days ago, and the staff has been discussing it since then. The new ruleset would remove some of the petty bans. For example, buying or selling Runescape items (not bonds) would no longer be under the 30 minute rule. Personally, I don't enjoy writing down times in a notepad to make sure rule 8 is followed, however it is the only way to keep track of the rule fairly as it currently exists. Eliminating all marketing from the chat is one solution, but I don't think it's the best option. Removing rule 8 is also a solution, but this creates drama. Having the staff ban people based on their discretion and non-concrete rules would not work out well.
As you can see, there really is no perfect solution. Sure we could lower the time in between messages. But would this even help? No, people would just continue to break the rules.
Right now, we do make sure to warn users before banning them, which I find to be rather nice.