Maybe also exclude messages by bots (e.g. "username has joined the server") from the index to decrease the stalking-potential of your site (99.9% of these bot messages have no informational-value for the index anyways). Currently you can still search for an username and get a subset of servers that the username is in (even if not active) by finding these bot messages.
This is something I have looked into. Unfortunately, every server uses a different format/bot. It might be possible to develop some sort of machine learning classifier to determine if it is a welcome message.