Push button start is there because it allows them to have the same dashboard on cars with and without comfort entry feature. I am indifferent between turning the key vs pressing the button. I did not pAy for Comfort entry it as I don't mind plugging the key in. I'd rather pay for features which are more useful. For example I love the new navigation. It's very sharp, fast to recalculate, has useful traffic data (At least on the way from spartansburg to ny it was very presize and uptodate, unlike my old system in the Acura). and it tells you expected delays and suggests time saving detours on the fly.
Rear camera is useful and really cool with the side views. By the way. cnet car tech did a video review of X5M where they show all of that if anyone is interested.