Ed,
I just did what you are thinking about: I bought a new controller (and other items I need) even though my white box and WGA work great. I am probably keeping my white controller as a back up (competitions) but I gave your question some thought when I was deciding whether to buy a black box.
I do not think there is much of a market for used Stokers. I would place the value on a used controller unit at 75-100 shipped. I give that range because there is no way I would buy a used one for 100, but I would almost certainly buy a used one for 75.
Relatedly, I have been looking for a used 10cfm fan, but nobody seems to be selling. I think most people would be more likely to sell a set up, for whatever reasoin, than individual components.