I could see Walmart being useful as a barometer, it'll definitely show you the bottom of the barrel. What Las Vegas is to money, Walmart is to civilized behavior. If the local Walmart doesn't turn your stomach it's probably a decent area. If you wouldn't want to take your kids in there for fear of them contracting a disease I'd look to another area.
I would not limit it to only Wally World. I would use the same reasoning on other chain stores also, specifically Kroger and CVS. Drastic difference between East and West side of Bloomington, for example. There is only one Walmart in town and it's on the same side of town that I'll drive by to shop the other side of town.