If I've learned anything from 13 years of moderating subreddits, it's that there is zero if not an inverse correlation between subscribers and quality. A community reaches a point where there's a healthy amount of content from a userbase that understands its culture and concept. That's its plateau. It can be a thousand people, ten thousand, even a hundred thousand. The number is arbitrary to a point and then the way people interact with content takes over. If people can digest one post faster than another, they'll upvote it faster and that will start to dilute the quality of the community. Images take precedence over text, templates over original content, popular over innovative.