a normal person writing term papers full time makes about as much as a teacher, ironically enough, but with no benefits and questionable job stability. it's the same curve, too-- you make less and work more at first, and wind up making more and working less. I like to see it as the inverse angle of teaching. though with a lot of teaching and professor jobs being farmed out to "assistants" nowadays, there may be no difference.
it will likely be a few years before you develop the contracts you need to make it full time, if this is your goal, so till then, I'd consider it extra income. that's what I do anyway; I think this is a silly thing to think of as one's career.
First of all, what do you mean by "develop the contracts you need to make it full time"? What essay writer has contracts?
I, like you, am in part-time mode. As for it being silly as a career ... well, on the one hand, I can't see a young person setting this as a lifetime career goal, it's true. On the other hand, if some writers are making 80k, and they like the work, then I can't knock it. Indeed, there are no benefits and you can't exactly advance. But that is the case for a lot of people nowadays, even if they might work in an office or other "real" setting. Stability is a concern, but in general, I would say the market for academic writers is strong and will be that way indefinitely. You're much safer if you have your own clients rather than relying too much on companies, though. Your real "stability" concern comes if you get sick and can't work. It's probably a small number of people who can pound out nothing but essays year after year, but I don't think it's exactly silly, especially if you love working at home.