Juliana, please don't worry about the question and discussions that followed your email. The reason why the thread became controversial and a long debate is because assessing articles quality has been hard for everyone I guess. Not an individual problem, but a movement problem for which nobody has the perfect answer.
I think some good inputs came out of this and that's obviously your call to decide the best way to grade your students. You've been constantly experimenting and this is important to find pros and cons of the methodologies you try.
Perhaps, establishing a minimum contribution (a complete paragraph with references? I don't know) could help you establish a baseline and you wouldn't have to be counting bytes (we can help you on this, but believe me, it can be hard, especially when they work in groups, or forget to login etc).