So there’s different types of users.
Some are interested in technology and want to discuss upcoming, real or conceived products, recently released products, and so eager to see product roadmaps and discuss unreleased products.
Some are purely here for free stuff.
The technology interest users are the ones you should seek to stimulate as they come and stay.
The ones just for free stuff vanish as soon as competitions ends.
The Powerbucks was a way for active users to get free stuff - so a reward for involvement, that should be restarted. Then competitions based on talent, which are difficult to admin but they filter out those purely milking the system for free stuff.
I’d keep away of “random winner” type if you can as they just invite multiple accounts and never do anything based on “likes” or “votes”.