For added fun, you can have the acclimation subtly affect those staying in it, having them pick up personality quirks and qualities reflecting the source of the BGC.

Yeah, and it somewhat works for that. Though aspected pretty much covered that anyways. The problem is, it basically removes any campaign setting pieces you might have for background count. The Chicago CZ effectively has no background count for the missions games if this rule is followed, sure specific locations might have a elevated or temporary spike you are not acclimated to but the setting piece is gone. Hell it may end up helping the PCs now unless you make sure to write in that all corporate raid teams you might go against in a land grab run or whatever are acclimated.