We can't fully upgrade all HQs in one city, without sandbox mode.
in my case, upgrading casino HQ and trade HQ is incompatible.
and for the level7 city hall, I need crazy 600 thousand population.
it is possible in only very few city.
nevertheless often I want fully upgrade HQ or city hall for surpassing limitations of the city concepts, beauty of the view... etc.
What about you?