Actually, the NRSC curve is about a +10db boost starting flat at 1 Khz and running up to 9.6 Khz. I think you have to be down something like 40 db by 10Khz. So there's a minor boost in highs, the idea being that it would help make it sound a little brighter on typical, rolled-off radios.
As far as better quality radios: HA! Back in the 80s when AM stereo came out, I called around looking for one. I had sales people telling me an AM/FM stereo radio was AM stereo.
It took me months to find a store that had the GE Superradio III, and it was a K-Mart of all places, not a major electronics store, and they didn't realize they had it, and had to dig it out of the back of a shelf.
People are stunned when I send them the YouTube video of the AM stereo Japanese station; I'm not, because I heard a Carver TX-11a receiver once and swore if there were AM/FM simulcasts, I'd never go back to FM again. (Turns out that has more to do with the 75us pre-emphesis and hard limiting on FM, but that's another post...)
The receivers WERE there. The technology WAS out there. By the time it came along, people were already mostly using AM for sports, news, traffic and weather, and saw no need.
I tried to convert as many as possible, but it was an up-hill battle... made worse by a lack of quality contemporary music programming on the AM band to demonstrate its capabilities.
AND THAT WAS NEARLY THIRTY YEARS AGO.
If I could wave a magic wand, I would have the FCC shut off digital, require 7.5 Khz frequency response & noise blanking in all radios, boost all AM stations under 50k to some higher power, start cracking down HARD on AM noise manufacturers, and mount a huge, expensive consumer education campaign. At the same time, I'd bring in AM station owners from around the country to discuss the technical improvements we were going to make to the listeners' experience, and encourage them to look again at musical programming holes in the market.
I don't see ANY of that happening. Even if it did, I think the AM owners would laugh me out of D.C.
I suppose if I could lobby the FCC for ONE thing, I'd push for the 7.5 Khz / noise blanking. That would do more to improve the listener experience than anything else.
If I had an AM stick... it would depend on where I was. If I was out in the middle of nowhere, I might be able to get away with AC / CHR / country if there were no local competing FMs and I had lots of community involvement.
In most cities above, oh, 25,000 residents, I think the only option is to find a secondary niche an FM won't or isn't filling.
The question I can't answer is whether a station targeted at a secondary group can generate enough income to pay the bills... although in the Tulsa, Oklahoma area (and many others I suspect) that's what's been happening.. in fact, right now we have FIVE Spanish-language AM stations on the air... and we'd have a sixth, save a dispute with a landlord. We have one, 6kw FM.
Years ago I heard an OKC station go EZ Listening / Beautiful Music. I thought it sounded awful, but I was young, the station was distant, and the processing could have been set "wrong."
Although it's an older target, I wonder if either Beautiful Music or Smooth Jazz could find a profitable home on AM, since they seem to be dying on the FM vine as the audience ages? This could be automated (pardon the pun) for a song, you'd only need maybe two employees and a sales staff, tops...