I'm not arguing that Dunn isn't a great value for us. That's the point. I love Dunn. But the FO has declared that they believe he is a DH, so he is not a long-term play. He's a great value for us now, but that is what makes him a great value for others. With Willingham able to play LF, dealing Dunn to a contender (and eating his salary) should be bring back some choice cuts in return. The guy is having a great year.
But why would he be worse next year? The Nationals, likely will be in the same position they are right now but, by not trading him until next year, they don't contribute to the idea that signing with the Nationals, as a free agent, means that you'll be shipped off six months later.
You become the Arizona Cardinals of Major League Baseball as far as a destination for free agents, the pre-Super Bowl Cardinals, that is.