Just to clarify, I'd say that the real point is to not have 'silos' of templates at all -- there should ideally be one repository of them, accessible anywhere messages are being written. If there is some mismatch in the tokens available (e.g. trying to use a template that references the current ticket number when sending new mail), then perhaps using those specific tokens excludes a given template from being used in a particular context.

Anyway, we use the same templates both for replying and for new messages, and keeping those templates synchronized is going to get rough over the long haul. http://en.wikipedia.org/wiki/Don%27t_repeat_yourself , etc.