The number of visiting fans will also depend on how good the visiting team is. Iowa and Iowa St have both been down for a few years, so that keeps their numbers down. Kansas is a national power with crazy fans, and with all due respect to WSU, I'm guessing a couple thousand KU fans would find a way into a game in Wichita. Indiana has a ton of fans, so they'll probably have a strong showing in Evansville, but there'd be a lot more of them if Indiana were still good. These games also bring out some people from the general community with no strong interest in either team, and it's hard to classify them.
We get football fans at basketball games when Drake hosts Iowa, and a lot of people show up wearing black and gold football gear and showing a vague knowledge of the game of basketball.