Even if you fully spec Yell, you won't see any good results. As it stands, Psi builds don't have enough points for dodge/evasion (nor do they see much use for it since they have their own damage avoidance spells), and other builds don't have much reason to allocate precious ability points into the otherwise useless Will. However, many do go for Strength (either as a main or side stat), and I think this would give some much needed synergy to dodge/evasion. This would also let a lot of builds take a social stat other than the always useful Mercantile.