How reliable are brake warning systems with regard to normal ware ? Nissan Murano with 63 K miles : the rotors look/feel fine. I expect to get at least this much mileage with discs and another 20 K would be OK, but I hope to get a warning before damage. Pulling off a wheel is half the work of doing a brake job; I have always done my own brakes but I am getting lazy. That is, if I pull off a wheel, I will go ahead and put on pads.
In my experience, the "squeal clips" sometimes work well, sometimes are very subtle, and sometimes don't work at all. You have to be able to recognize the sound, and it occurs gradually so you may adapt into thinking it's normal.
The "red light" BRAKE on older cars is usually a combination of parking brake lever sensor and master cylinder reservoir level. It doesn't provide much information about the actual state of the wear surfaces, unless the pistons are so far out all the fluid is in the car and not the reservoir. Lube shop mechanics tend to "top up", which renders this diagnostic useless most of the time. (It's on their checklist, after all.)
The third yellow "warning triangle in the drum" is present on many German and some newer Asian cars. This can be an indication of any number of things:
The sensor wire embedded in the pad(s) wearing through (or just coming loose or breaking, bad connection, dirty connection, etc)
Something with the hydraulic portion (low fluid, bad pressure feedback, etc)
Something wrong with the ABS, which will light the ABS warning but often (e.g. Honda) also lights the yellow brake warning triangle at the same time
Your Murano is a fairly heavy vehicle with large brakes. Without knowing your driving habits and style, 63K miles is a very good run for any set of rotors (especially original), and 83K indicative of someone that drives ever-so-gently. Frankly, I would not hesitate to replace rotors at 63K, regardless of their appearance. It simply does not make sense to do the labor for a pad change and ignore the rotors. Furthermore, I like to bed new pads with new rotors - but that's a personal preference that not everyone shares. Decent rotors can be had for $75/side, so the thought of "making do" or getting them "cut" is pure folly in my opinion.
I consider brake pads AND rotors, spark plugs, all to be in the same category as oil changes. "Just do it" is a trademarked phrase; I don't care what the owner's manual says, what the $12/quart oil jug says, or wive's tales near and far from learned mechanics and mere ingenues. The cheap will come out expensive. YMMV.
On the other hand, careful monitoring over your continued driving will prevent any "damage" you might be concerned about. If you get to 80K on the current parts, a backing plate grinds and scores rotor(s) and you can certainly detect that; rest easy knowing that you got another 17K and you would have had to replace the rotors anyway.
I'm as cheap as they come, but I prefer to think of myself as "smart cheap". I'll push as long as I can, but if I'm doing other maintenance at the time, now is the time to do pads AND rotors. I never do pad slaps (unless the customer absolutely insists, and signs off on any warranty), I never replace one strut, I never replace one tie rod end, I never replace one wheel bearing set, I usually replace both CV axle shafts, and I do oil changes at regular intervals even if it "looks clean". If one part of twins is failing due to normal wear and lets you know, I almost always do the other side.
It's my philosophy and it's certainly not universally accepted. But as you mentioned yourself, getting the vehicle in the air and the wheels off is half the work. Why risk repeating the same effort 5K later?