To answer the original poster's question:
-Flagstaff is at about 7000ft elevation, and studies have shown that to be just about ideal for optimizing the effects of altitude training. Going up in elevation is always a tradeoff between the pros (increased oxygen carrying capacity and greater aerobic stress while running) and the cons (more difficult to recover, slower running at the same intensity), and 7000ft yields a pretty good - maybe the best - combo of the pros vs to cons.
-Access to lower elevation - one of the ways to mitigate one of the cons of living at 7000ft is to do at least some of your training at a lower elevation (so it can be at a faster pace at the same intensity, better simulating racing at sea level). From Flagstaff, places like Sedona, Camp Verde or even Phoenix are doable. This also comes into play if/when Flagstaff gets a lot of snow in the winter. You can just drive to lower elevation to get out of the snow and into warmer weather.
-Training venues - There is a huge variety of good training trails, roads and tracks in and around Flagstaff. There are lots of single track trails, especially in the mountains. There are lots of forest service roads. There is the FUTS (Flagstaff Urban Trail System) of mostly soft-surface trails that connect through town. There are a couple of high school tracks, NAU's track, and NAU's indoor track. Access to the HS track in Sedona famously (and hilariously) became more difficult, though. Marathoners especially seem to like Lake Mary Rd as a place to do marathon-specific work on pavement.
-Balance - Flagstaff is a small city, so there is "stuff" around - decent medical resources, entertainment, jobs, etc. However, it is small enough that running can still be THE THING for people that go there for it. In other words, there is enough going on to stave off most boredom and/or make a living, but not so much that you get distracted.