The retainer is the cap piece that [along with the keepers] form a taper fit place for the top of the spring to press against. And no, you generally wouldn't want new springs and retainers unless you went with wilder cams.

Also, qtiger's right, a 5 angle valve job usually causes more chance of wiping the valve seat, or cracking a valve near the edge since the number of angles cut into the valves mean that the edges are normally thinner.