Since the basic SEIV is something like 100 stars, 8 nations, and loads of other low settings that many of us might not even remember; I will certainly think of it as an expansion
But you are probably right. Add-On might work for sales.
Whoever wants to do the work can upload it to CafePress on a free account and let people go there to buy it. Id have no problem paying 10 or 20 dollars for it. And it certainly wouldnt bother me if the person got some dollars for the work.