Now here's the problem with both of those libraries:
Wallpapers:
Because a decision was made a while back to lower the minimum accepted quality level, more walls were accepted, most of which were essentially unusable. There have been more Vue scenes uploaded than I've ever seen before, thanks mainly in part to the change in moderation.
OD:
Like A_67 said, many of the icons that are uploaded are just cut-and-paste images with "jaggies", etc. These are unusable. I'm not really sure why icons such as video game boxes and cut-and-paste logos are accepted at all, bu the majority of recent submissions have been pretty low-calibur stuff. That being said, we can't all be Jairo or Farid, tho (

), so the submissions won't always be top notch like the work of the two aforementioned members.
The Main Point:
Will OD ever reach the popularity/size of the Wall library? Definately not at this rate. Until moderation returns to normal in the wall section, the walls will reach 10,000 before OD even hits 5,000. But if we do decide to raise the moderation on the Wall library, we should also raise moderation on the OD library as well.