Well, I think that I may have the answer. It will add something to the actual Green Skies in the way of background BUT it will not be a "must buy" -Black Tower policy has always been that you buy a book then it is all self-contained (but, obviously, not the anthology titles!) and you will not have to buy this or that tie-in issue.
Just as you will not have to purchase the Dr Morg book to get the connection (I'll explain it all as we get closer to publication day) with this epic so this will be a treat.
Trading card still seems like an idea.
Now, off to work on more pages.