For a good while I've considered that I haven't highlighted enough, though I did a recent project that I considered was over-highlighted, but when the dust had setttled this was not the case at all. For a good while, I have used complimentary shading as well, and this does help and is a fascination learning curve as well.
Overhighlighting can be very useful in conveying a sence of urgency and drama to a figure and is worth considering for this alone.
As ever, it's all about experimenting and learning as you go along....
Janne, many thanks for that link - it was a fascinating eye-opener!