It's all about programming, of course. All about YOUR ability to build an audience (and the station's ability to properly promote). Imagine being the first voice on the new FM station in town in the late 40s, when very few people had FM radios.
There ARE a couple of HD2s with live human beings around (though some by network) in my area. If your station is serious enough to hire real people for the HD2, then hopefully they're serious enough to promote it, including on the main channel. If I were you, I'd take the challenge. But then I believe that AM radio is still viable for more than just right-wing talk and preachers. People listen to PEOPLE!
It won't be easy, but if the station is realistic about what to expect, and you're patient, and persistent, then GO FOR IT! Realize, however, that we're talking about VERY "delayed gratification". It may be YEARS before your audience is substantial, even under the best circumstances. This is FM when everyone had only AM. This is TV when there were TVs only in the stores, and the stations were only on 6 hours a day. It's virgin territory!