The way I interpreted Drac's point is that
non-reproduction cels are the basis of something
tangible. Production cels -> videos. Hanken cels
-> magazine covers, posters, trading cards, pencil
boards, etc. Game cels -> games. Repro cels -> ...

All items related to a series inherently promote
the anime, and repro cels are no different in this
regard. It is that, as cels, they did not help to
produce anything beyond fan interest.

---Trebuchet