While I agree that a lot of pressure can be placed on the American’s early. Let us not forget, that under certain conditions, it is possible for the U.S. to upgrade any of its minor factories. While I think this is wasteful, it can be a tactical decision based on first impressions of the Japanese players first round position and builds.
If you plan to sail your fleet over to the Pacific from the Atlantic, then Upgrading W. US seems wise. This enables a large build on round 2, when the starting Atlantic fleet is in position to reach W. US sea zone 10. This should give you a fleet that rivals Japan when they attack turn 2 or 3. I never move to Hawaii, without placing a blocking destroyer in sz 25 or 16, unless I feel secure. Blocking DD’s are why the US should build 1-2 a turn in a Pacific campaign. In some games, I’ve used as many as 4 blockers to enable a strong board position or to prevent counterattacks on islands I wish to support with air units on a following round. Blockers typically draw out a sea unit as most people are loathe to trade planes for DD’s. Permitting a counterattack of that sea unit later rounds.
If you plan to hit Europe, and suspect an invasion of W. US, you can upgrade Central round 1, and build a large take back force, assuring continental independence. A Major on Central serves two purposes, defense of W.US and it enables the creation of large land force that is able to shift to the E.US if Germany forgoes London for Washington on turn 3’s maneuvers.
As I struggle with finding game balance in A2, I find more and more axis techniques that really challenge the allies in such a way, that defeat seems inevitable. When I iron out “Operation: Stützpunkt” (Operation: Fulcrum), I’ll post an axis win based on a 3 turn Neutral USA, no sea lion, 9-10 turns, and an 8 city victory.