(3) Could a whole city or nation, or world, be themed with multiple themes?
It is possible, but the themes would not be stable. The theme effect demands contrasts to everyday life. If everything is themed, but with different themes in different places, then the ordinary would be that there was always some theme. The themes would be "what you do here: you have to present yourselves as Roman here, and as Disney characters there." It would be difficult for this to remain a theme as it would soon become just a set of appropriate social roles or actions for various places. Aristocratic behavior at a party or lower class behavior at a bar are not themes but grammatically normative roles and attitudes.
(c) David Kolb, 1 August 2001