Here's how I'd tweak GST: First, I'd get rid of the forced doubling and multi-day format altogether. It seems like the doubling is an unnecessary way of making athletes emulate Michael Johnson, and it has the risk of burning out or injuring athletes before their most important meets of the year. Plus, it's hard enough to get fans to come out to one day of track action; there's no need to try to get people to attend more than one day for a non-championship meet.
My recommendation is to organize it as a three-meet series: One on the west coast of the U.S. (but not Eugene), one on the east coast of the U.S., and one in Europe, in a country that doesn't already have a Diamond League meet (perhaps Spain, since Valencia does such a nice job with its road races). Things in 3s are more digestible and easier to remember, and it makes for better event group creation, as illustrated below. It would also allow for even bigger prize money at each meet.
I'd organize the event groups as follows, with each of the three meets having just one event per group:
- Short sprints: 100, 150, 200
 - Long sprints: 200, 400, 600 (or maybe 200-300-400, I'm torn on this one)
 - Short distance: 800, 1200, 1500
 - Long distance: 3k, 5k, 10k (or maybe 3k-5k-8k or even 3k-4k-5k if there are concerns about event length)
 - Hurdles (just one hurdles group): 100/110h, 200h, 400h
 
That format would result in nice compact meets with 10 races per meet, which would be good for both live spectators and television viewers. Having each event group race at a different distance at each meet would keep the series interesting by avoiding repetition from one meet to the next (how many people really want to see Hocker, Kerr, and Nuguse race at 800m multiple times in a year?).
Prize money would be awarded for each race at each meet, with additional grand prize money for the top 3 of each event group at the conclusion of the series, based on their placings/points throughout the series, including a special bonus for everyone who completes the entire series (as an added incentive to not skip meets).
Keep the racer/challenger format, because that can create compelling and unique matchups at each meet.
Create a third group of athletes called Transcenders or something, consisting of athletes who commit to running the entire series but aren't limited to one event group. That would allow the most versatile athletes like Sydney and Tebogo (if they could sign him) to transcend boundaries by racing any event they choose at each meet, making it even more likely we get the special matchups that fans want to see.