To an extent I agree with the above. Almost certainly the glow plugs will be shot and the swirl vanes will be leaking diesel. When you take the inlet manifold off to correct these issues it is a ten minute job to fit the blanks. The question is do you risk not doing so?
My personal experience is there was degradation in performance without them which I later regained by removing the dpf. I have seen others reporting increased performance/economy without the vanes but this was not my experience.
As for flap failure on e90 six pot it probably happens as no one seems to be quite sure what size they have in the manifold. The smaller spindles had issues for sure. Mine were 32mm but has anyone found the 22s in an e90?