Yoda, Force Spirit is a very interesting unit. Representing Master Yoda after he dies and becomes one with the Force, he is immaterial and can’t directly affect the things around him. Yet, to the Force-using units on your squad, he acts as a walking Force battery. Not only does he grant Force Renewal to any one Force character (which is crucial — far too many units with awesome Force powers are lacking the ability to recharge), he lends his own Force points to any Force user on your squad. Since Yoda, Force Spirit has Renewal, he provides a constant supply.
His one weakness is that he is easily dispersed by an enemy Force user. This might not be a bad thing, since you get that enemy to waste Force points on it, but probably not what you want to spend 20 build points on. On the other hand, if you’re pretty certain the opposing squad is not using the Force, a small band of Jedi feeding off of Yoda’s Force could be pretty amazing.