I was actually reading an answer to this in an old Astronomy mag this morning. What Rick says was the response - basically no.
They did comment however that if there was an increase in local dust there might be a dimming of distant stars or very faint glow from some parts of the sky.
Up on Maleny during XMAS hols there was a day we drove up into clouds (really more like fog). From outside the clouds seem very thick, but once inside you can dimly perceive the moisture moving past and distant views disappear. And that would be an incredibly greater density of matter I expect versus a neb.
I wish the damned moisture over the top of me right now would disappear dammit....
