Devel user & decrease number queries
1) By default, dblog module is enabled. It is real performance bottleneck for big sites. But you can use syslog module (from core) or contrib analogs to write logs in /var/log/drupal.log and etc.
Rsyslog config can be something like this:

    local0.warning /var/log/drupal_site_err.log
    local0.info;local0.!warning /var/log/drupal_site.log


You should analize your logs and fix errors, warnings and even PHP notices. I think 281 messages per page — this is a lot.

2) On your dev site you can allow anonymous users to see devel information with permission “Access developer information”. Don't forget to disallow Devel on production.