In the mining example I gave it's probably more clear cut than the SV case. A whole heap of people are working high wage jobs in essentially the middle of nowh

In the mining example I gave it's probably more clear cut than the SV case. A whole heap of people are working high wage jobs in essentially the middle of nowhere. The local towns don't have the capacity to replace many lost jobs and aren't the ideal place for all of the now unemployed workers to end up. You don't want a whole heap of empty houses in an area with no jobs. Diversifying the economy is definitely a step in the right direction and is likely more feasible in an area like SV. On the flipside you've got to be careful that the other industries are valuable in their own right and don't exist solely due to the rivers of money in the area.