Our metaphors cohere. But what Lakoff and Johnson did not state clearly is how there might be a discourse between metaphor and culture. Though the polar oppositions up-down,in-out, etc.
When a government thinks of its enemies as "turkeys or "clowns" it does not take them as serious threats, but if the are "pawns" in the hands of the communists, they are taken seriously indeed.
Since communication is based on the same conceptual system that we use in thinking and acting, language is an important source of evidence for what that system is like. We can actually win or lose arguments. I wouldn't stoop to that.
You're running out of time. To address that problem, three forthcoming books cover much of the same ground as MWLB, but in more scholarly detail. The CONDUIT metaphor does not fit cases where context is required to determine whether the sentence has any meaning at all and, if so, what meaning it has.
A more interesting approach is that taken by Hobbs and by Rumelhart.