Re: High kicking
I typically use low kicks. Occassionally there is the perfect opening for a high kick, spinning kick, or skipping side kick that is just there.
I learned a great deal from my Karate days about mid distance and control.
Watch the UFC, a usually see a few higher kicks than you'd think would be practical thrown.
I have been successful with kicking grapplers in the head. That said, I would be very careful about high kicks as you are planted longer and more off balance than from a low kick, which can translate into a takedown by your opponent.
It is important to have a good arsenal of weapons. High kicks do belong in that arsenal.