Thanks for entertaining the question, I in no way expected some precise measurement. I did think about your last point too, and sort of came to the conclusion that maybe the milky way's stars, being so much closer, would account for the vast majority of the visible matter, and at any given moment would block out a huge part of what's beyond. Then again I would think that the Hubble images show the halos of the stars, not the matter, and there would be waaaay less of matter than is apparent in the photos. Being in intergalactic space would probably change things a lot. I'd already be willing to accept the 30ish% for intragalactic. I thought about this first a long time ago as a kid watching star trek/galactica etc, how likely is it to hit something when moving at warp speed.