Heya GBalkie,

These voids don't have clouds or nebulae blocking the view because the superclusters of galaxies beyond the void are clearly visible (with the relative distances of all the visible galaxies beyond the void mapped by redshift).

These voids are intersupercluster areas (bigger in scale than intergalactic space) devoid of galaxies, and by extension devoid of stars because gravitation tends to cluster stars into galaxies.

But yes I agree that there might be things too small/faint to be seen in these intersupercluster voids. Guess we'll find out for sure in a few million (billion?) years should the human race develop means of instantaneous intersupercluster travel assuming we'll still be here for that long. :)
The scale is very humbling.