Fordranger, you're forgetting the one key mantra of music radio (tongue only partly in cheek here): LESS IS MORE.
Instead of having 5 Tom Petty songs in rotation, you've got to reduce that down to just 1 and pound away at it -- but make sure that one has been researched to a fine crisp.
It's the same with the other 90's stuff. Even in Seattle, arguably the home of the biggest and best 90's rock, no one apparently cares about Soundgarden's extensive array of radio hits, you've got to hammer away at the biggest one, which probably researched well.
This is how you get ratings. Unfortunately, this is also how you drive listeners to Spotify and Pandora. 35 years ago, Radio could operate with the 'less is more' mantra and not worry about losing listeners to other platforms. Today it's different. The methodology for ratings success is the same, but unfortunately for Radio the listeners have other options.