I definitely noticed a difference in the chalice dungeons with insight. I was stuck on a boss in a Layer 4 chalice for two days. My insight was at 99 so I decided to spend it and go back with 5 insight. Holy crap it was like night & day. After I got rid of my insight I was able to take down the boss I was stuck on, as well as the rest of the Layer 4 & 5 chalice bosses.