I do think there is a critical mass for getting followers: once you have enough high quality content, followers keep coming automatically. I see this all the time on profiles of people who have left HubPages months ago.
I don't see the point in making multiple accounts if you are here to earn money but some people do have multiple accounts. Whether you have your affiliate codes associated with this account or some other account does not matter, you still need to get those view and clicks.
I don't know anything about the growth of one's earnings over time so I cannot answer your question about proportional growth.