Personally I quite like lunging, I don't use it very often or for very long but I find it useful. It helps my mare improve balance and also improves her response to my voice cues which in return improves my flatwork. Currently I'm trying to encourage her to bring her head into a comfortable outline position, often I school alone so I can't judge exactly if her head is correct or too tucked in. Lunging helps me to monitor her progress.
I just think it's one of those things that some horses respond well to and others don't, if you find it works for you then happy days!