Primal Scream at 9:30 was just about empty. That was one of the more sparsely attended 9:30 shows I've been do, along with Charlatans UK a couple of years back.
Past shows...
V Fest last year seemed pretty empty to me. Maybe that was just perception - but I could walk up to the first few rows for every set.
One of the best I've ever seen was Azure Ray/Crooked Fingers at the Black Cat. There were probably about 50 people upstairs for the mainstage show, maybe 100 tops. Amazing set.
Now Its Overhead at IOTA was very empty.