You already did open up your content, but personally I'd lead with that. Make lurking free and any interaction part of the subscription. This would include posting content, as it does remove the most blatant spam and gaming of the system.
Having said that, while I do think it is commendable that you want to reward the people that provide content, I am not sure if you should do so based on votes. Because that will just make it so people will try to game the system with clickbait and fluff content.
As we are on HN anyway:
"The Fluff Principle: on a user-voted news site, the links that are easiest to judge will take over unless you take specific measures to prevent it."
Source: Article by Paul Graham (the guy that started HN and funded reddit way back in the day) http://www.paulgraham.com/hackernews.html.
What this means is basically the following, say you have two submissions:
1. An article - takes a few minutes to judge. 2. An image - takes a few seconds to judge.
So in the time that it takes person A to read and judge he article person B, C, D, E en F already saw the image and made their judgement. So basically images will rise to the top not because they are more popular, but simply because it takes less time to vote on them so they gather votes faster.
Some things out the top of my head you can do to mitigate this are:
- Don't tie it to voting, make it a different action people have to explicitly give. Basically reddit gold, but then still with the monetary reward tied to it. - In addition to that, don't make it an infinite resource people but a monthly budget people can spend (this might already be the case? I didn't check too closely) - Technically a bit more challenging, but if you could tie it to engagement time in addition to votes it would mitigate the fluff content issue somewhat. Some metrics you might be able to use are time spend in comments, time between clicking on an outbound link and voting (don't count votes with no outbound interaction either), etc.
As a seperate thought, I am not sure if there are liability issues when you reward posted content with money. Not all posted content will be owned by the person posting it, but they are effectively being paid for it. So that might make you as a platform more liable for copyright claims and such. Not a lawyer though, just something I thought of.