Again, I propose doing it twice per year. I'm not 100% sure how many people participated this year, but I can imagine people (like me) unfortunately missing out on it because of work, two-three times in a row. In addition while there was some advertising of the event I'm pretty convinced a lot of people didn't know about it. By having it more often more people can get wind of it and participate.
As for the location: I think if you decide now where to have it and choose an area that's not done, then the airports etc need to be developed. Unfortunately - and I don't intend to criticize people - we can't rely on that to happen. People say they will contribute x,y,z, and then real life gets in the way and either nothing is done or it's too little. I really don't think it's wise to select an area where there would be a need to develop a bunch of airports (you mention six!), because that's a lot of work to do and a lot to rely on having to happen.
I think it makes more sense to pick a region where airports are already relatively good looking. The US west coast area of KLAX/KLAS/KPHX is a pretty good example. And there's still room for both improvement on those airports I'm sure, as well as smaller ones around the area. And speaking of the area I once again push for a varied landscape. With the US west coast you get the ocean, desert, mountains, the grand canyon, rivers etc.
But I think South America could be a good choice if there's an area that is similarly densely developed. Or the Caribbean. Or England.