Can't really answer you questions directly.
But, my wife is an amateur photographer.....pretty good at it.
She takes action shots (surfing, skiing/snowboarding) and stills (nature, ocean, landscape, people, etc.) with her regular camera (Nikon).
She has a GoPro 3 Plus and LOVES it. She got the housing for underwater, etc.
I will say it takes amazing video AND still shots.
I read somewhere that there is a new competitor for Go Pro (forgot the name)....supposed to be pretty good, but having over-heating issues and such, and it's almost as expensive.
A $30-$50 knockoff will "work"........but it won't be nearly as effective in many areas.
Guess it just depends on what you want your final product to be, and what your needs are.