Gearhead, I like what you've done. I have a scratch in the lower area of one of my bags, that starts below the bottom-most "rib" and runs through the area that's already texturized. So in my case, just coating the top third wouldn't help. I'm seriously considering entirely coating both bags.
Anyway, I don't know anything about wet sanding. I wonder if you could give a little more detail about what sandpaper you used and how you did the sanding? Did you do all the sanding with 400 grit, or did you start out with something more coarse and finish with 400 grit? Was it just your basic 400 grit paper that I'd buy at any hardware store, or do you need some special type of sandpaper to wet-sand plastic? Did you do the sanding by hand, or did you use a machine?