Ya, it's a double edged sword. You want people, but the right people 'Better fewer but better.'
Over the long term, without relying on gimmicks to try to get orgfags over, the best way to attract a base of people is just to post more.
I'd divide posts into two categories.
A) Effortposting longer pieces
B) lower effort shit posting/banz
It's the appropriate type of content for the format of an imagneboard
It really is content that is it key. If you had a blog or leftoid newsletter and you wanted to build up the readership/traffic, the same would apply, posting regular content in the form of longer form written content, just with a bit lower velocity.
>It's really that simple, lol