Cedar Rapids doesn't have enough latinos to support a station. Didn't work in Sioux City with a much larger Spanish-speaking population; the audience was there, but the ad dollars weren't. If anyone would do it, it would be CC on 1360, and that's highly unlikely considering their experience in Sioux City. Best bet for Spanish would be time-brokered, somebody buys the airtime and sells their own spots.
Cumulus must be making money on KRNA despite the low ratings. The numbers are only for Linn County, they don't include Iowa City, so maybe KRNA has a big audience there? Or they have advertisers convinced there's a big audience in IC?
Of course, the big hole in the market is Hot AC, thanks to CC's dumb move to country on 96.5 But Cumulus is unlikely to put Hot AC on anything because it would hurt KDAT. Switching the CHR to 94.1 and putting talk or sports on 107.1 might make some sense. But KRNA has had bad ratings for a long time and they haven't changed it, so the ad dollars must be OK.