Thanks, Allan!
Those dust streamers are most intriguing. David Malin et al (
http://arxiv.org/abs/astro-ph/9407074) talked about a "boiling galactic disc" in which star formation, supernova explosions, and magnetic fields might have produced these vertical streamers. Later work at ESO seems to favour star formation only, but it's a bit technical for me to understand, and they're more talking about carbon monoxide than dust.
So which bits are the streamers, exactly? I've indicated on the attached image some very long, relatively narrow, orange-brown streaks rising approximately but not exactly perpendicular to the plane of the galaxy. I'm guessing that these are they. It helps to screw your eyes up (but not shut tight!!) to see them best. Then they are very obvious. There are probably twice as many as I've shown, but these are the best ones. The ones closest to the galactic core (upper left) are about twice as long and three times thicker than the ones further toward the suburbs (bottom right). They are definitely not part of the spiral structure, because they are more or less at right angles to the spiral.
Best,
Mike