I don't disagree with any of you from a straight-up value perspective, which is why my first question in the description was too much, and not too little.
With that said, I was trying to think of it in terms of what Dallas would actually take, and what Washington (may) be actually willing to give up. If I'm Dallas, I'm looking at my depth chart in both the NHL and AHL and thinking that it might take quite an offer to make me move Roman Polak up to my top four. I will admit that I'm not super well-versed in their prospect pool, but it doesn't appear that they have anybody ready to move up and assume top-four minutes for the next several years, so I think they want a defensive prospect in return. I think that Washington is willing to part with Siegenthaler because they have Johansen, Ness, Hobbs, and now Fehervary coming up in the system, with Bowey just about ready for real minutes, plus they get a younger defensemen in this trade to begin with.
With all that said, I think this hinges on two things: what is the long-term plan with Niskanen, and how ready to you think Bowey is? Johns could be a good interim solution, but I could definitely understand the argument that the need isn't even there if you think Bowey is ready next year (he isn't this year, plain and simple).
What about Burakovsky and Johansen, with no pick? Or Burakovsky and Bowey (either rights or a sign-and-trade, gasp!)?