Hmmm. Interesting query. I'd say "Yes," but with reservations. Personally, if it's about "revenue" - I don't think making a market three-times the size with HD2 & HD3 is going to make much different. The revenues won't be there or the main channels will run into problems, IMHO, as listeners turn to the HD channels.
I've been told, however, that "Results" iare a whole different matter. If few listeners actually went to retailers, service businesses, etc. and continually "bought" -- then you don't need a 6-share to be successful. "Less is More." I've been told that if a station has an audience of, say, 500,000, but another station has an audience one-fifth the size, but the one-fifth audience regularly responds to advertising vocally to advertisers on that "niche" station (no matter the demo) stations can be very successful that way.
Maybe not in the David Eduardo stratosphere, but successful, nonetheless.
Ask yourself: If Station "A" had 1000 listeners according to the ratings and Station "B" had 10 listeners, but they regularly bought products and services that you knew came only from advertising on that station, what would you feel? Would size of audience matter if you were moving product?
I bet a lot of stations pitching huge cumes are being asked, "Then where the hell are all the listeners? I sold only 3 this week..."