Yeah, this is something I don't see a lot of other folks doing, or at least I don't notice it. I use several kinds of pen or ink. The brush and india ink are great for fills, and solids, and the ballpoints do a good job with textures and shading. I tend to do just enough realism to make something recognizable but I feel that the getting it to close takes some of the magic out of it. If I deviate to much from reality it becomes a mess. It's a real tightrope walk sometimes.
I think you do a great job of stylizing while still keeping your subjects recognizable. (I tend to get bored with tightly rendered realistic portraits -- especially celebrity portraits, although folks just go gaga over that stuff, I shudder at their lack of creative vision... lol XD )
I have a few theories about that. I think art brains see the world in a way that none artistic people just can't grasp through no fault of there own. That's why clear communication skills are as good to train for an artist as the technical, and imagination building stuff. I am really interested in the science behind art. How perception works and all that.