I don't possess access to that data. I agree it's the angle KCI officials should be giving voters. Most I have are direct quotes from airline officials saying they don't land at KCI and prefer to go to st Louis to connect passengers even though it costs them more to do so. To which clams will now try and misdirect with some hair brained MDW comment.
You shouldn't fight their battle so vehemently unless and until they help you out.
The arguments I'd be using (if true) are:
1) W/o a new airport, ______, Inc. is going to leave here and cost KC ____ jobs (or w/a new airport, ______, Inc. is going to come here and create _____ jobs).
2) W/o a new airport, KC will lose out on a [convention, sports team, etc.] that will preclude KC from having $_____ injected into the economy and ______ jobs created.
3) W/o a new airport, ______ Airlines is going to leave (or reduce flights) which will reduce travel options to ______ resulting in (______ of increased travel time and/or ___________ in higher average fares).
There's probably some other direct $ factors that could be argued for the KC scenario. I'd also consider, if it exists, putting in a point about how the airport, as the first and last thing visitors see, affects impressions of KC and any effect that might have on return visits or even "tourism." And if there's data that would show there's enough people like me who avoid flying to KC when there's any other option, enough to make any sort of $ difference, add that too.
I'm with you that the KC airport is lol embarrassing, but for locals who've become accustomed to it and use it as nothing more than a necessary thing to walk through between their car and the plane, that aspect doesn't matter.