I have no idea about prices, either new or second hand but I think it is pertinent to remember that some of the most collectable pieces were not popular when they were first issued. Look at the Daytona for example, it was unpopular because of the manual winding movement and now look how much they are worth. So, from a purely financial point of view I believe that rarity is the key. I don't know how many of these green milgauses exist but if they are rare then in years to come they will surely have their day.
All the best with the decision.