I think forums are doing it right. A lot of forums call it
Resources and allow all or premium members to download digital products. These could be graphics, plugins and addons, themes, ranks and badges or almost anything someone would want to use. Even wallpapers would fit fine into this Resources pool.
But the bigger challenge is to verify these downloads. Malware is one solid challenge, the people could steal other people's work and share it as their own.
Do you have a Resource pool on your website ? Is it helping you gain premium members ?