My EDC surefire E1e with KL-4 LED head is over 7 years old now and I haven't needed to replace the LED portion yet....and this is a light they gets used almost daily. With that being the case, I haven't found it necessary to carry a spare LED portion, just batteries.

With that being the case, it is still a good idea to have spare complete LED flashlights around. Modern flashlights are getting smaller and smaller for their output, so it's getting easier and easier to misplace them.