No "new" format is going to displace a successful, well rated "old" format. So the idea that AA failed because the stations were not previously garnering good ratings is absurd. I've done several successful news-talk startups and none was on a successful station. Two went on to be #1 in their markets and another... coming from a 0.3 went on to tie or beat KFI in 25-54 quite regularly.
Advertisers had no client dictates to not buy "progressive" talk. They had some client dictates not to buy anything controversial ranging from Stern to Limbaugh. That is why you would have agency accounts on KFI in Dr. Laura that did not run any other time.
"Selling a station properly" is the worst cop out ever. If a station has low ratings, irrespective of format, it will not be easy to sell. And the prices will have to be commensurate with the audience delivery. Nothing you say can change the fact that it is easier to sell a top station than one near the bottom.
As to signals, many of the Air America signals, such as Miami, Portland, LA, Seattle, and quite a few others were viable. Even the much improved WLIB in New York would be able to compete with entertaining, compelling programming. Air America was simply not interesting. Good programming often overcomes signal disadvantages; the current #3 25-54 station in San Francisco does not cover 60% of the market.
It's funny that the post mortem of formats that "should have worked" all have the same "they did not do it right" in the statements. When Pulse failed to succeed with dance in New York, it was mostly blamed on the music selection...