When i run as an undead I'm pleasantly surprised when a monster heals me with negative energy. The key point is surprised. It happens so infrequently that i am rather skeptical that increasing the damage by NEB will have any impact. Keep in mind that when I'm healed by mobs its just as often chill touch or the negative ray and neither of those are going to be changed. I would expect changing how this spell targets (it fails to cast if you target is not in touch range) will have a much bigger impact on player experience.
I expect others who play undead will agree with theses observations.
Your point about self selected people reading to this thread is spot on however.