This is a suggestion that came to my mind: give a user who shared some resource 1 or 2 credits when other people unlock it.
Right now there's "quantity over quality" rule: you share more stuff, you get more credits, regardless of the quality/value/rarity of the content.
If people knew that unlocking their content will give them extra credits, they would be interested in:
- sharing more valuable/rare resources,
- making better descriptions and previews ("promoting" their resources).
I'm already happy of how credits are awarded now, so that's just an idea to think about or discuss