Spirit Seers seem like a bit of waste to me, thier only advantage is not allowing 'Wraithsight' within 6", but I usually but a Warlock in all my Wraithguard units anyway. Are they worth having?

(I know what they have their Ld increased to 10, but seeing as Wraithguard confer fearlessness to any joined charcters anyway, it doesn't make a difference.)