I'd tend to agree that smaller towns, less affluent towns with quite a few everyday sort of cyclists in street clothes are usually nice places to cycle. That's the way Carson City, Nevada is. I've heard several long haulers surprised at how friendly the town is. Move over to Reno, which is about three times the size of Carson City and things change. There, it depends on the neighborhood and infrastructure with some areas quite friendly and others not so much.
As for the poor areas of town, I keep an eye out for how much bike and foot traffic there is vs. groups on the corner and '4 riding low' in a older car. The more dangerous areas have more cars and less (or few) out traveling on foot or bike.