Depending on the state of your plumbing, and the number of people in the house, it really may be a good idea to replace the valve with either a pressure balance (less expensive) or a temperature controlled valve. One or the other of these is now required for any new construction or replacement. You can still fix your old one, if you can get parts (which you should for the Delta), though. Either of these has some real safety benefits over a standard valve assembly.
I first experienced a temperature controlled shower valve in London. Liked it so much, bought one for my current remodeling project - works great. You set the temp you want, and then just turn the water on. The same every time - no futzing around if your are the 2nd or third one to take a shower and the tank is getting colder - it just adjusts the supplies on its own and (trys) to keep the water the desired temp. You'd never have to worry about getting a hot or cold spike, either. The pressure balance valves prevent hot spikes, but do nothing to keep the temp the same if the supply starts to run out of hot water. Course, it doesn't heat it! But if you are often the last of a train of people taking a shower, then it makes the best of the situation automatically for you.