Road Atlanta is a great track, and would be much better suited to F1 than Laguna Seca. I think the pit complex and access roads would be the only things needing major upgrades to host a GP there.
Road America would likely be decent, too, except for being in the middle of nowhere. Like Magny-Cours, it is just too far away from anything. And Magny-Cour had the twin advantages of being the President's pet project and the FIA being effectively French (especially under Balestre).
And that is kind of the problem for F1 in the US - and much Europe. Many of the "classic" European tracks are a bit out of the way.
Notice how most of the Asian rounds are all either right in or very, very close to huge populations - Singapore is right downtown, Shanghai is close to the city and Kuala Lumpur is next to the airport. Snagging 100-150,000 people for an event is a cakewalk for these cities so the gate is always packed and the promoters have a very good shot of making their money (doesn't hurt the government picks up much of the tab, as well).
Back when Senna drove for Honda the Japanese had to hold a lottery to sell tickets for Suzuka (part of the reason they added the Pacific GP). His death in 1994 and Honda's departure in 1993 meant that, eventually, Suzuka didn't even sell out. Between Toyota owning Fuji and Fuji's proximity to Tokyo, I am not surprised Fuji was added to the calendar to alternate with Suzuka.
Just as has now happened with Germany now that Michael no longer races. They used to be able to support two races, now they can only support one and have to alternate it between the Nurburgring and Hockenheim (which was neutered to allow more people to watch the race).
As much as I miss the party atmosphere that was ending the F1 circus in Adelaide, I imagine Melbourne does better thanks to the larger population base. And Valencia has that "hip vibe" that F1 so loves, which means that if Spain needs to drop to one race, it could survive instead of Barcelona.
But even being downtown isn't a guarantee. Mexico City and Montreal were downtown. The former left almost two decades ago do to a bad track, but Champ Car rebuilt it so that is no longer an excuse. And now Montreal can't make the numbers work. Maybe they should run it on the Vancouver or Toronto streets like Champ Car/IndyCar.
I think when the US GP comes back, it will be at some place like Las Vegas which has enough cash to make it happen with real permanent facilities like Monaco, Singapore and Valencia all have.