Yeah, but what's it mean to be human?Replacing your biological body sure has effects on your personality and perception of the self. As you become less human you probably also feel less human and you would feel less like yourself. Imagine looking at yourself in a mirror and all you see are prosthetic parts, a foreign element that you now call yourself even though you know it's not really you. It's like waking up one day in an entirely different body than you were born in. That would fuck you up in the long run, I'm sure of it.
And if we're talking cognitive enhancements then it becomes even worse. Your personality comes from how you interpret events in the past. Those interpretations aren't really accurate and they are definitely biased; It's your brains version of reality and that has shaped you into the person you are today. If you have a perfect memory there's no telling what that would do to your personality. There would be no room for personal interpretation, you'd have perfect and factual memory of every event in your life, it would just become stored information.
So yeah, I don't believe it would require a lot to destroy our current personalities.
It opens up a whole other can of worms, that one.