@Joe Doran I'm interested in this as well. I grew up in Johnson County (Olathe) and currently live in Northern Kansas City, MO. I am fairly new to the real estate market and don't have a ton of experience, but I'd at least like to share my thoughts!
The housing market in Johnson County is extremely aggressive right now (like it is everywhere I suppose!). One thing that I would be concerned about is the ROI and cash flow on properties in places like Overland Park, Olathe, Mission, etc. Cash flowing $200/month on a property in Jackson/Clay County that cost $150K, vs Cash flowing $200/month on a property in Johnson County that cost $350K seems like a much better ROI, especially if you are having to put 20%+ down. I also wonder what the rental/owner percentage is in the high dollar subdivisions in OP and Olathe. Seems like the majority of the people that live in those houses own them. I would think in the older neighborhoods and subdivisions there would be great potential, and like you said, the A-class and upper B-class neighborhoods are more plentiful than in most of Jackson County. Another thing that I'm assuming would be more standard in the area that would hurt your cash flow are all the HOA's and their fees.
Clearly Johnson County has a massive rental market because there are as many apartment complexes as there are banks (and in Johnson County that's saying something!). As far as Single Family Homes and Multi-Family homes go, I haven't really been interested in looking there. I'm sure there are investors that are making a killing there, hopefully they chime in!