I own both a black and hard chromed bolt. As far as a difference major difference, other than the obvious, I have not observed real differences in they way the perform and function. They (hard chrome) may be a little easier to clean. I think they originally intended chrome bolts for use it harsh combat enviroments like vietnam. As far as my HC bolt goes and I'm will to assume most everyone on this board, I shoot in a relativly sterile enviroment. That is no blowing sand and dirt, no excessive moisture and I certainly don't use corrosive primers like they did years ago. As for the extra money, sure they look cool in your rifle, but a standard "black" one will suffice and likely give you years of trouble free service provided you do your part to keep it clean.
HTH