Hello:
I have noticed recently that there's extreme CPU usage even when LogView is completely idle, that is more than 50%, not having any logs open, not having any applications running.
What's going on?

LogViewPlus polls the directory for changes.  Depending on the number of files and directories being monitored, it might cause a problem.  What happens when the directory is not monitored?  Does performance improve?

There is no way to exclude older directories.  

Yes, this helps, thank you. 
It would be great to be able to filter monitored directories by mask.

Glad that helped - thanks for letting me know.  

Filtering by mask is a good idea.  This is something we could look into for a future release.