I've lived in Utah my whole life and been at high elevations but never experienced elevation sickness until we drove up there in a hurry. We had a bag of potato chips in the backseat that exploded on their own due to elevation increase. Still an amazing trip.

Kona is fun. Hilo is the only place you will get any of the lush green that you might expect from Hawaii. Maybe you will see Dog the Bounty Hunter over there too.