What specific system messages are you seeing that should be ignored, specifically?

Item searches are deliberate, for example. Why would you need them if you never invoke /isearch in the first place?
Show recommendations have their own 'don't show me this' button in character configuration, as do those related to available achievements.
You can turn of a lot by going through the character configuration panels. No problem.

And where, oh where, did you read or hear about 'amazing customization options' for system messages in the general chat channel?