Why should there be spam ingame, and why would you encourage that?
No one wants to see raging people express their hatred on who they just lost their TC to (bet/duel) or a couple of people using the broadcast system as an IRC channel, regardless of if it collects TC.
I doubt there's any need for TC to be taken out of circulation at the moment, and even if there were, the community would have to be in a complete recession for users to be allowed to pay to express their idiocy in the form of a global.

Broadcasts were specifically designed to announce in-game events. The power of saying anything you want to hundreds of people at a time would be overwhelming and the system would be abused.
EDIT: A more indirect way of doing this, however, is a system we already have; bounty hunting with the optional 2,000 TC bounty text.