I've gotten shots like this and I don't think you're doing anything wrong. Your exposure settings seem fine based on image metadata at 3200 ISO, 15s. I'd imagine you need to find a place with less light pollution - yes there was a distant city in my picture, but that was a pretty small tropical city on an island. And I was on what was basically a deserted island with minimal backlight and (very) clear skies due to the location. I hear people get good shots in the desert as well like Nevada. Further, you might be shooting the tail of the Milky Way galaxy here although I can't tell from the shot. Make sure you're getting the galactic center - I remember getting a shot similar to yours when I hadn't aimed the camera in the right direction even while in the BVI.
As for the Glidecam, I find the Glidecam HD-2000 works and some people even use the HD-4000.