I understand you want to encourage people sharing, it is obviously a sharing site lol But unfortunately most people just want to take without giving anything back, thats how the world is now 🙁
My ideas for that is collecting more points for sharing things, just an idea but say 100 points for posting something, then 50 points when someone downloads it, thats insentive for people to post. I do also like the idea of gift card rewards, I know I would certainly do everything I can to get those lol just my ideas 😀