Mine were clean as a whistle before I put on protectant, mostly because it was cold enough I was wearing long sleeves all the time
Now that it's short sleeve season, they do get a bit of dead skin in them, I find it brushes right off though. Worst case I take a lint roller to it.
did you notice the fabric becoming more coarse, like gunmetal did with the scotchguard, after the 303?
Didn't really notice any difference. Carpet in the trunk feels pretty much the same as well. I didn't bother doing the cabin carpet, too much work!