If we are talking about most people flying in - then we might want to discuss 'hubs'. That reduces the number of connections for many passengers, and thus can reduce price.
Major hubs in the center of the country:
Toronto Pearson International Airport (YYZ)
Dallas-Fort Worth International Airport (DFW)
Chicago O'Hare International Airport (ORD)
Lambert-Saint Louis International Airport (STL)
Houston George Bush Intercontinental Airport (IAH)
Cleveland Hopkins International Airport (CLE)
Salt Lake City International Airport (SLC)
Cincinnati-Northern Kentucky International Airport (CVG)
Denver International Airport (DEN)
Milwaukee General Mitchell International Airport (MKE)
Kansas City International Airport (MCI)
Minneapolis-Saint Paul International Airport (MSP)
Detroit Metropolitan Wayne County Airport (DTW)
Memphis International Airport (MEM)
From Wikipedia:
For non-hub cities and low cost flights, Southwest Airlines (WN), a low-cost airline, mostly runs point-to-point service, but has hub-like operations in Baltimore/Washington International Thurgood Marshall Airport (BWI), Chicago Midway Airport (MDW), Dallas Love Field Airport (DAL), Las Vegas's McCarran International Airport (LAS), Houston Hobby Airport (HOU), and Phoenix Sky Harbor International Airport (PHX).
In terms of driving, Kansas City is close to the center of the country - but is it close to the center of the AK membership? In other words, the 'west' is more sparsely populated that the 'east' part of the country, California excepted. So there could be potentially more AK members who might attend AKFest on the eastern side of North America than on the western side.
One can also consider Amtrak - a great way to go in my opinion.
www.amtrak.com will give maps of the major hubs for Amtrak.
We might also consider locality in the sense of what we might do other than attend listening rooms. I realize that in the past, we haven't, but what if we held AKFest in some major city that also had a current or historic audio equipment manufacturer, where we could arrange a tour? Just a thought...