I don't lunge to just get the willies out of her. I use it to work on things, and get her thinking. I work on transitions, slowing and fastening the trot, canter, and walk. Direction changing, backing up with diff cues, to get her really tuned into my body language. So I don't do it to run energy off her. I just use it to get her thinking, and work on some other things as well. I have rode her before without lunging, and while it is perfectly possible, she is much more in-tune and enjoyable after it.
Never let "good enough," be good enough.