Are healing items really that necessary? Ninpo & Ki do good enough jobs. Even on Master or Ultimate Ninja. However, I feel that Obliteration techniques should heal some health along with the Steel on Bone's.
I'm not that good at the Ninja Gaiden games, but at least when I'm fighting the bosses I'd like to be able to heal myself when they start bullshitting me
Which bosses are giving you trouble? Remember to learn their attack patterns and act accordingly. Razor's Edge is based around trying to take as little damage as possible from bosses through cautious and smart play.