As you well know, speaking voluntarily (even to the government) and under compulsion are two different things. By this standard, nearly every criminal defendant's invocation of the Fifth Amendment would be "clearly disingenuous," because many trials contain both "voluntary" statements by the defendant to law enforcement and invocation of the Fifth Amendment. I don't think any negative implication can or should be drawn. Lerner's most criminal behavior was likely related to her trying to appease conservatives by claiming the IRS engaged in "absolutely inappropriate" activities in response to a planted question.
This is the IRS scandal that wasn't.
Pretty much. I don't think anyone could ever invoke the fifth amendment again if we are going to go by the republican definition of waiving the right.