Hi Jeff,
As you mentioned we can only aggregate same message that occur within 60 sec max.
It sounds like what you are monitoring is being trigger excessively.
If some of theses message are none critical would advise either diverting them to a external syslog server or to not trigger them at all.
Another suggestion is if messages are originating for the APs you aggregate the messages being forwarded to the controller to see if that helps a bit.