I run around with 15-20 insight anyway, I just like to have a backup in case I lose it.
Also, I don't like magic much. Its all about doing as much physical/fire damage as you can in as short of a time as you can. I swapped the tophat for the plague mask anyway. Also, that chick sounded like 80, so...... Oh, and little tip for the witch of hemwick lane. Just kill her, ignore the minions. They are easy to dodge and the fight goes quicker that way.