Ellen, I couldn't agree with your first sentence more. Some of the most grace-ful moments I have had in therapy with people have come only as we struggled with impasses or empathic failure. When handled well, they help the patient rewrite scripts and bolster my self-confidence. They have been the most touching, deeply human parts of the therapeutic dance.
At times, especially when working with folks with trauma histories, it is a heck of a revelation for the patient to realize that I will admit I am less than perfect, hear and acknowledge their feelings, and display caring for them despite the negative affect in the room. It can be particularly stunning with dissociative disorder patients. Suddenly it dawns on them that they/I can feel shame and I still care. Not only do I handle my shame very differently than the abuser did---(most abusers were in the attack-other script library of the compass of shame)---but I also care about what the patient feels. The more intense the affect, the quicker, it seems, we rewrite the script. (It can take a lot of repetition.) My patients have certainly taught me a great deal!
Tomkins' theory and Don Nathanson's work on shame have been marvelously helpful in my work with patients.