Hey Leaf,
From my experience, it is very hard or near impossible to keep that pencil type texture as you vector it. If there is actually a process that I am aware of, I would love to learn it too. It would be extremely helpful to my workflow too as I always lose the sketchy feel of my sketches when I transfer from sketch to ink to vector. But if there is a vector version of the sketchy look, it would be so memory intensive as the program has to account for so many points that is making the texture up. I do not think illustrator has a plug in for this either.