I 100% agree on sanding. I had to do this for areas of my shadow stormtrooper years ago. Obviously, if it's been painted, then you'd need to strip that and see how the plastic, but since I was working with black ABS, sanding worked great. You want to sanding pads that essentially run up to like 12000 grit. Others may have recommendations for where to start, meaning you don't have to start at the lowest grit necessarily and work your way up. You may be able to start in the middle. What I would do is find a spot that you can sand the inside of the armor or a spare piece and go through stepping up the grit until you get to that gloss finish. I will also wax mine periodically with Maguire's. Worst case scenario is you can go the paint route in the end, but it can be tough to get it even. I had an auto body shop do a different set of armor pieces to get it right.