Don't underestimate lurkers. Subreddits I moderate all have atleast 100 lurkers for 1 poster. Most people are just in for the content. A read-only membership would allow them to filter the content to their needs. Which is big enough reason to create an account with 3 clicks and providing username and password, but not enough reason to state an mail, gender or even ask and wait for allowance.

Quality posts requires effort, why should one invest time in it, when there is only a limited amount of reputation to gain?

So you don't like the invite system but don't want to get rid of it, either? It's not like we can do it halfway — it's either invites or no invites.

First Idea, just for the sake of the discussion:

Read-only memberships, 
with an upgrade option, who requires an invite to allow posting.

Gives people a trial option and creators more reassurance when there follower count grows. You could also spin it further, as a monotizing option: Invite or 1$ for write upgrade. Yes, has is disadvantages too.

I don't mean that the invitation system should go away or that it is bad per se. Just that it is a too big entry barrier for a specific set of people, from which snapzu could gain.

Fandoms of that type are mostly full of shy people who try to socialize by using a common ground on which there a comfortable with. Those are kind people, who can't even really lurk on this site, because they can't even follow tribes or people.

While people who will hurt snapzu intentionelly are not stopped by an invite system.