We could make community packages of quality artwork (audio, wallpaper, themes) but it is a bit difficult to define 'quality artwork'. How do other community-based distributions like Ubuntu manage this? The idea is (to me) that, we decide purely on the quality of the artwork, and after that, discern and imagine a first time user uses the artwork in question. The power user will feel OK searching further.

Not knowing about Ubuntu as GNOME (or FD.o) user there are several options. One can browse e.g. Gnome-Look.org and there are various ways to sort artwork. The Maemo section is very much out of date, btw.

Anyway, even if no packages for extras(-*) some kind of centralization is still useful. If not only merely a wiki entry with the howto & pointers.