And yet another idea in desperate search of a theme

Here's a few ideas:

Town Hall/Local Government Politics
- Policy formation and compaigning followed by election

Some kind of market speculation or market driving e.g. oil speculation or commodities
- Gather inside information/generate market leading rumours followed by purchase of shares on the market

Advertising or Product Marketing - try and determine which product is going to be the next big thing
- Propose, develop and test products followed by testing them in the market
- products could be anything - financial products, cosmetics, fashion, cosumer electronics

In fact, thinking about all the above the freshest theme would seem to be 'fashion designers trying to make a splash with their new collections and determine whats hot and whats not next season.

Drunken Backyard Baseball - Pulling together enough sober family members, neighbors, and friends to make a halfway decent team each inning, followed by how well they play.

Most of these suggestions are theme of existing games, but that could apply to your game:
- Japaneese Warlords strugling to become shogun, making alliances with groups, using ninjas, merchants, geishas, gaijins and samurais to "push" their influence.
- Machiavelli: During the renaissance era, merchants would push their influence on politics to expend their empire.
- Prince of Thieves - Internal power struggle within a guild of thieves.

I think "market/shares/oil/speculation" concept proposed by TheReluctantGeneral is quite interesting as well. If you are looking for a humoristic theme, you could build your game around super hero girls struggling for the "sexiest/trendiest/fashion-est" super hero suit. Players would bid on suit parts such as cape, boots, mask, bra or whatever part of their super hero suit they wear, to improve their reputation (The one with the most flashy suit would make the newspaper frontpage).