On Kansas City, it feels like a little bit of everything in the US as the people come from all corners of the US. But the golden years (late 1880s - early 1900s) of the city were definitely Midwest/old world influenced and therefore much of the older part of the city has those attributes.
Look at these early pics of KC. Seems to look more midwest than west or plains or southern. Appears closer to a smaller Chicago/Detroit than a Denver or Dallas or Memphis or Atlanta.
http://forum.kcrag.com/index.php?topic=2788.0
In pretty much every case, the KC media portrays KC as part of the Midwest. According to the Feds in most cases, the Plains begin about 60-100 miles W of KC but KC and Denver are considered to be economic centers for the Plains. Denver city is technically in the Plains while KC metro technically isn't.
Being from St. Louis, KC feels Midwest but not part of the Great Lakes region and most KC people are a bit more W Coast laid back than most of the Midwest. There's some southern black culture influence but not much more than most other midwest cities. There are also more Mexicans in KC for obvious reasons while the eastern side of MW would likely have more Cuban/PR Latinos in most cases, Chicago the exception.
Oddly, the geographic center of the US is somewhere in Kansas, so the region we're talking about technically should be called The MidEast. But the term may have been coined when Chicago was the western population center of the US.
BTW, when I was in Columbus they didn't consider OH to be midwest but rather eastern, being in the eastern time zone I suppose. But they considered Cincy to be southern.