There is no need to have springs and retainers unless you want to rev higher than the stock redline. If you do rev higher than the redline on stock springs you could end up having floating valves and ruining your valves and pistons due to contact. Oh and if you plan on adding some wilder cams... you should also upgrade your springs and retainers even if you don't rev past the stock redline.
If you decide to keep your stock cams and don't plan on reving too high... save your money and don't get the springs and retainers.