The only calibers that I neck size for are the ones in my tight neck custom rifles that I have to neck turn for. There is a positive difference there. In a factory rifle, the difference may be very small or even none at all. I have not seen any difference with case life, as the necks either splits or the primer pockets get loose.
Neck dies are not real expensive, so sometime when you have the extra cash, get one and try it out. I have a few of the Redding 3 die sets that include a neck die. I find that I don't use the neck die, but the set is a little cheaper than buying a separate die later. I'll probably start a fight now, but I don't feel that a bushing die offers a lot unless you neck turn. Another opinion of mine is that bushing dies are not a good thing for a newby to start with. (Flame Suit On). Lightman