Logging levels apply across the board. Are you constrained by disk space? What do you mean by "online extract"?
What we do is that we take a backup of the logs every night via tabadmin ziplogs and then clear the day's logs via tabadmin stop tabadmin cleanup tabadmin start.
Yes, we started with similar approach of taking backups every few hours and dumping it to our nas storage for further analysis using logshark and other tools. We recently started shipping all our logs to splunk and it is a much better experience to filter the log based on a given request or session id (you can grab the session id using chrome dev tools).
If you need the regex to retrieve the key fields (custom fields in *****) then look at the source code of logshark on github.
I have no problem filtering the logs after they were created. I would like to avoid the logging altogether (of specific views).
I am constrained by disk space. I prefer not to log some data, rather than maintain cleanup processes. Is there a way to avoid specific views from logging?