There is one thing that matters more than any other in making a sport popular: Already being popular. Basically it's the Matthew effect. People watch sports because other people are also watching. It gives you a feeling of community. It provides a topic of conversation. It also FEELS like sports are really important if other people around you care about them. So obviously we're a very long ways from a world in which you can talk about track around the water cooler. But there are things we can do if we keep in mind the cardinal rule that if you want someone to watch track, you need to make them feel like other people care about track.
First, the announcers are effing terrible. They need to be losing their minds with excitement. If these pro commentators can't even muster excitement, it conveys to the viewer that what's happening really is pretty boring.
Second, you need to focus on growth within smaller communities where you can more easily create a critical mass of people who all watch, and can therefore discuss with each other. This is basically athletes. You need to get high school and college people really watching, but you also need to get adult recreational runners, especially the more serious ones who may be members of clubs.
You might also look at how European pro soccer grew in the US, through pubs. Even if you knew nobody else who liked soccer, you could always find a soccer pub where the handful of people who were into the sport gathered. (Interestingly, the hardcore soccer pub is less of a thing now because you can now see soccer pretty much anywhere.) USATF could try to get one pub in every major city to be a "track pub" that commits to showing all the major meets.
I think the majors is an interesting concept because it's the right frequency to have real fans without demanding too much of them. Tennis and golf are never going to be the NFL, but a lot of people will watch 4 times a year. Heck, a lot of people will watch horse racing 3 times a year. By contrast, having important competitions in 3 out of 4 years just isn't enough to sustain any kind of interest. The problem with the majors concept is that they (and the triple crown) all developed organically. People have cared a lot about these events for a long time, and as I said above, it's the other people caring thing that makes you care. I don't see a viable way to tell people to care about these events because "these are the big ones now." That's the Diamond League and Golden League basically. The reason the World Marathon Majors sort-of works is that they took races that were already a big deal and just formalized their status.
So basically, I think that fiddling around with the product itself should continue, but it's never going to be the main driver of interest in the sport.