Implications of not using any diopter on an X Pro-1?

I bought a second-hand X Pro-1 last week and it's missing the diopter, from what I understand the stock diopter is just plain glass with no correction so from that perspective not having one will make no difference to the viewfinder image but I'm worried about having the viewfinder area/optics exposed to the environment which may allow the ingress of dust etc?

Is that a valid concern or not?