I agree with the above poster. Adam Goucher's 13:10, 3:57i, 7:41i, and 10:50 4k win are pretty amazing for someone who is 31(was 30 for the 5k time).
As far as what Hall should do, I think he should run the 12k. I think it would be good preparation for him for the future, seeing how there will be no more 4k races at worlds, and the talent in it isn't as good as in the 12k, so the 4k wouldn't really be as valuable a measure for how one stacks up internationally in distance running. However, I think both teams would have a fair shot at medaling. Goucher, Lincoln, Hall, Torres, Dobson, and Watson could fair pretty well I think. Torres, Goucher, and Watson are experienced at the 4k race; it would really be a matter of if Hall, Lincoln, and Dobson stepping it up. However, reserving Torres and Hall for the 12k team wouldn't be bad either. I think the USA will have a good team eitherway, Ritzenhein's health pending.
From an earlier post, I would agree that it is funny how quickly everyone jumps on the Hall bandwagon and the anti-Ritz bandwagon, which for some, is the same wagon. The only person who knows what's wrong with Ritz is Ritz himself and maybe his coach, hopefully. I just hope that when it comes time for worlds, the guys that are representing the USA are the best guys to be representing the USA on that day, and I think the top 6 in each race are probably the best 6 to do so. It would be interesting however to see how Goucher would fair in the 12k, if that were a possibility. In the 4k, Torres has placed 11th and 13th, Watson has placed 38th, and in the 12k, Gabrielson and Ritz have some experience. I think the USA could place in the top 5 in either race. I don't think they could beat Kenya, Ethiopia, Eritrea, or Qatar, but I could see them beating Uganda, Algeria, Spain, Portugal, and some other top 10 performers. I'll bet the USA places 6th in either or both events.
As far as what I think Hall should do in the future, as if what I thought really mattered, but its fun to think so, Hall should work on his mile speed. If he can get down to a 3:38/3:39 this year, I could see him going 13:04-13:06 this year, but I could see some others doing that as well. Ritz, Dobson, Torres, Broe, and Goucher.