I had a close one on the Alpina, my MOT man failed it on the brake pipes he could see (and admitted he had been harsh) but was concerned about what he couldn't see. So I had him also change the metal papes front to back. When done he rang and said if ever he had felt vindicated for using his experience and gut feeling this was one of those times, the pipe running front to back and over the fuel tank, was totalled knackered and could be snapped like a twig, I was the one who snapped it when I got to the garage. The pipe was a few hard brakings from blowing.
IMO when it comes to brake pipes don't just worry about what's visible, if the exposed ones are that bad I would assume the lot is nearly as bad. It may be an expense but what's a few quid against hitting the brakes at 60mph and finding they have left the party?? Tyres and brakes, probably the most important parts of your car.