I agree that these sets should stay the course. Anything that sells out immediately is doing something right and there will always be folks who are unhappy whether a product is too short printed or overprinted(hence what they buy has no future value).
I'll second that they should stay the course.
Though, I would suggest that changes made along the way for the last couple of series, like multiple "bio cards", or the lack of an unlimited version set - do not serve the long-term viability of the series, and should be dropped. If not, additional changes, for example a subscription plan, should be instituted to help ease the negatives associated with those mentioned added wrinkles.