Having lived in both San Francisco and now back in my hometown of Wichita, KS, I always enjoy when I can talk about both places within the same topic.
As far as urban decay, guess where you'll find it? You'll find it in urban areas 100% of the time, per the very definition of "urban decay". To claim that local phenomenon are a direct result of local political leanings is to play very fast and loose with cause and effect. I can think of ten other hypotheses off the top of my head about the cause of urban decay, many of which don't factor politics in at all, and some of which actually involve inverting the cause-and-effect relationship of your own hypothesis that liberal politics cause it (maybe urban decay causes liberal politics?). To put it generously, it's utterly obtuse to say, "urban environments often include blighted environments, urban environments often have liberal-leaning voters, thus liberal politics cause urban decay, case closed."
I should also mention that these same urban areas do not consist completely of blighted, impoverished neighborhoods. Every city has it's good parts and its bad parts. But I'm sure the devoted partisan will find some way to assign a city's bad aspects to whichever wing of politics they don't like while simultaneously claiming that the good parts are actually somehow proof of the correctness of their preferred politics.
So on to Kansas. Right now in Kansas, yes the cost of living is very low, but the lower average income from what I see does not at all work out to the advantage of most people. The only people who can really take advantage of the low cost of living are the few people here such as myself who can work remotely and thus take advantage of the sorts of incomes offered by industries which don't even tend to locate here. Here in Wichita alone, in the midst of Governor Brownback's conservative libertarian "business friendly" policies in full swing, Boeing just up and packed its bags and left the state entirely, leaving huge swaths of longtime residents suddenly jobless. Where did those jobs go? Many places, including the supposedly anti-business liberal hellhole of Seattle. So it seems your simplistic reasoning falls apart at the slightest examination.
Kansas is a fairly deep red state, and right now Governor Brownback has a lower approval rating here than President Obama. That takes a lot of fucking up to achieve. Even my grandma and my great aunt are posting to Facebook with calls for his resignation at this point, and they both tend to espouse strong conservatism both socially and economically.