I would strongly suggest you clean what is there and paint it. Tearing it off will create a good deal more work and covering it will be nearly impossible. Painted brickwork can really look nice, I like what you are describing with the glossy black. I've done this recently with some chimney areas. As you said the key will be to clean it well. I would advise TSP (tri-sodium phosphate) and a soft bristle brush to scrub it well, then a good masonry primer. Your best bet is to go to where the Pro's shop, a real paint store. Tell them what you want to do and they can get you the right stuff including a thick roller to better cover all the masonry.