> cowboy boots are associated with (mostly southern) rural areas
Your expression seems to become less meaningful as you clarify it.
Cowboy boots are part of Western wear. The specific style (as differing from general equestrian boots) started during the cattle drive era of Texas, Oklahoma, and Kansas in the late 1800s.
It spread, certainly. Cowboy boots are a much more salient aspect of Montana, New Mexico, and Wyoming - decidedly non-Southern states - than Virginia, Florida, or North Carolina. What cotton farmer, tobacco farmer, or citrus grower works in cowboy boots? The traditional Florida cowboy wasn't even called a "cowboy", which is the western term, but a cowman or cracker.
I'll say this again, they are indeed called cowboy boots, which means they come from the area where there are cowboys. That's the West, not the South. (The two areas overlap in Texas and Oklahoma.)
So 1) are cowboy boots a salient feature of rural life in the US? No. They are not common to rural life in Michigan, New York, Maine, and other non-plains states.
2) are cowboy boots a salient feature of the rural south? Based on http://www.newsobserver.com/living/fashion/article10118804.h... , at least in North Carolina it is the suburban population which buys the most cowboy boots, not the rural population.
3) Is the south the area where cowboy boots are the most salient feature? No. That would be the West. In the South you buy cowboy boots at places which sell Western wear. You don't buy cowboy boots at a places which sells "Southern clothing."
On the other hand, in the West, where cowboy boots are a salient feature, you are also likely to find people in the cities wearing dress cowboy boots with a suit.
So "cowboy boots" means someone from the West, and "suit" means someone dressed formally, "suit and cowboy boots" means someone dressed formally in the Western clothing tradition.
While "suit not cowboy boots" tells someone in the Western US to dress in the standard US/European business tradition.
But "cowboy boots not suit" makes little sense as a disjunctive. It certainly doesn't characterize someone from the rural US, or characterize someone from the rural South in the US, with someone from the city.