When Did "Get" Become "Be"?

Recently I was on website devoted to education, where the author suggested that teachers "Get creative."  I bristled. Not at the idea, but the phrasing.

When did "get" become "be"?

Somewhere between the 1980s "Get psyched" and the 1990s "Get amazed."  Or do we need to go back to the early 1970s and the Partridge Family's "Come On, Get Happy." Or even further to the depression era tune by Arlen and Koehler, simply "Get Happy."

In all of these phrases, "get" is a verb that should mean "acquire," and therefore, I expect a noun not an adjective to follow. As in:

"Get creativity."
"Get excitement." (I'm guessing at a rather homophonic aural morph from "excited" to "psyched")
"Get amazement."
"Get happiness."

Okay, so these phrases are not the stuff that advertisers or cheerleaders are going to bark any time soon.

The problem is not really with the adjectives, it's with the verb. "Get" has taken over "be."

How does this happen? Perhaps there is something existential going on here.  After all "get" is much more aggressive than "be."  "Get is active, and "be," well, being intransitive, it just is.  The zen of be first, do second, and have third, comes to mind. "Get" puts us in reverse.

I fear, though, in this acquisitive consumerist culture, I'm on a loser.  But maybe we can "be creative" and discover something we can do to save "be," and save "get" for those things to be had. 

For certain, I would  be excited, be amazed and be happy if we could.