Yeah I try to avoid "midwest" at all, except when being vague is a goal. The distinction between "Great Lakes" & "Great Plains" seems quite useful both geographically and culturally and "midwest" seems to just splotch right over that boundary.

I agree with your western boundary, though I'd probably just call it "The Rockies" myself, and let Nevadans and Utahns get absorbed either into "West Coast" or "Southwest" as they personally desire.

This system does create some problems for e.g. Missouri & Arkansas, which are in the confluence of 3-4 other regions, and you have to accept that Pennsylvania and New York get cut in half, but it's what my brain has settled on.